IRS Notices - SAF (reporting, third-party disclosures, and recordkeeping)

Part III – Administrative, Procedural, and Miscellaneous

Section 45Z Clean Fuel Production Credit; Registration

Notice 2024-49

SECTION 1. PURPOSE
This notice provides guidance on the registration requirements for the clean fuel
production credit determined under § 45Z of the Internal Revenue Code (§ 45Z credit). 1
A taxpayer must have a signed registration letter from the Internal Revenue Service
(IRS) dated on or before January 1, 2025, for the taxpayer to be eligible to claim the
§ 45Z credit for production starting January 1, 2025. Thus, taxpayers should apply for
registration as soon as possible to give the IRS sufficient time to process registration
applications. See section 4.01(2) of this notice for additional information. The
Department of the Treasury (Treasury Department) and the IRS intend to issue
additional guidance on other aspects of the § 45Z credit at a later date.
SECTION 2. OVERVIEW AND BACKGROUND OF THE § 45Z CREDIT
.01 Section 45Z generally. Section 13704 of Public Law 117-169, 136 Stat. 1818
(August 16, 2022), commonly known as the Inflation Reduction Act of 2022 (IRA),
added § 45Z and amended §§ 38(b) and 4101(a), 2 enacting the § 45Z credit for

1 Unless otherwise specified, all references to “section” or “§” are references to sections of the Internal
Revenue Code.
2 Under section 13704(c) of the IRA, these amendments apply to transportation fuel produced after
December 31, 2024. See also footnote 4.

-2transportation fuel produced in the United States by the taxpayer at a qualified facility
after December 31, 2024, and sold by the taxpayer to an unrelated person in a manner
described in § 45Z(a)(4) during the taxable year. For purposes of § 38, the § 45Z credit
is an amount equal to the product of (A) the applicable amount per gallon (or gallon
equivalent) with respect to any transportation fuel which is produced by the taxpayer at
a qualified facility and sold in the manner described in § 45Z(a)(4) during the taxable
year and (B) the emissions factor for such fuel as determined under § 45Z(b). See
§ 45Z(a)(1).
.02 Applicable amounts, emissions factors, emissions rates, and provisional
emissions rates. Section 45Z(a)(2) and (3) provides the applicable amounts for
transportation fuels. Section 45Z(b) generally provides the rules for emissions factors
for transportation fuels used to calculate the amount of the § 45Z credit. Section
45Z(b)(1)(A) provides the rules for calculating the emissions factor for a transportation
fuel by using the emissions rate for such fuel.
Section 45Z(b)(1)(B)(i) directs the Secretary of the Treasury or her delegate
(Secretary), subject to § 45Z(b)(1)(B)(ii) and (iii), to publish annually a table that sets
forth the emissions rate for similar types and categories of transportation fuels based on
the amount of lifecycle greenhouse gas emissions as described in § 211(o)(1)(H) of the
Clean Air Act (CAA) (42 U.S.C. 7545(o)(1)(H)), as in effect on August 16, 2022
(emissions rate table).
Section 45Z(b)(1)(B)(ii) provides that in the case of any transportation fuel that is
not a sustainable aviation fuel (non-SAF transportation fuel), the lifecycle greenhouse
gas emissions of such fuel is based on the most recent determinations under the

-3Greenhouse gases, Regulated Emissions, and Energy use in Transportation model
developed by the Argonne National Laboratory, 3 or a successor model (as determined
by the Secretary).
Section 45Z(b)(1)(B)(iii) provides that in the case of any transportation fuel that is
a sustainable aviation fuel (SAF), the lifecycle greenhouse gas emissions of such fuel is
determined in accordance with (I) the most recent Carbon Offsetting and Reduction
Scheme for International Aviation (CORSIA) which has been adopted by the
International Civil Aviation Organization with the agreement of the United States, or
(II) any similar methodology which satisfies the criteria under § 211(o)(1)(H) of the CAA,
as in effect on August 16, 2022.
Section 45Z(b)(1)(D) provides that in the case of any transportation fuel for which
an emissions rate has not been established under § 45Z(b)(1)(B), a taxpayer producing
such fuel may file a petition with the Secretary for determination of the emissions rate
with respect to such fuel (provisional emissions rate). The Treasury Department and
the IRS will provide guidance regarding the emissions rate table and provisional
emissions rate petition procedures at a later time.
.03 Registration and unrelated party certification requirements. Section 45Z(f)(1)
generally provides that only registered production in the United States is taken into
account for the § 45Z credit. Section 45Z(f)(1)(B) provides that, for purposes of
§ 45Z(f)(1), the term “United States” includes any territory of the United States.
Section 45Z(f)(1)(A)(i) provides that no § 45Z credit will be determined with

3 Section 45Z(b)(1)(B)(ii) refers to “the Greenhouse gases, Regulated Emissions, and Energy use in
Transportation model developed by Argonne National Laboratory.” The name of that model was changed
to “Greenhouse gases, Regulated Emissions, and Energy use in Technologies,” and as of December
2023, it is generally referred to as “R&D GREET.”

-4respect to any transportation fuel unless the taxpayer (1) is registered as a producer of
clean fuel under § 4101 at the time of production, and (2) in the case of any SAF,
provides (A) certification (in such form and manner as the Secretary prescribes) from an
unrelated party demonstrating compliance with any general requirements, supply chain
traceability requirements, and information transmission requirements established under
the CORSIA described in § 45Z(b)(1)(B)(iii)(I), or in the case of any methodology
described in § 45Z(b)(1)(B)(iii)(II), requirements similar to the requirements described in
§ 45Z(f)(1)(A)(i)(II)(aa)(AA), and (B) such other information with respect to such fuel as
the Secretary may require for purposes of carrying out § 45Z.
The unrelated party certification required under § 45Z(f)(1)(A)(i)(II)(aa) is required
as part of a claim for the § 45Z credit for the production and sale of SAF. The Treasury
Department and the IRS will provide guidance regarding unrelated party certification for
claims for the § 45Z credit at a later time.
SECTION 3. DEFINITIONS
.01 In general. This section provides definitions that apply for purposes of this
notice. Section 3.02 of this notice provides generally applicable definitions. Section
3.03 of this notice provides definitions related to non-SAF transportation fuel. Section
3.04 of this notice provides definitions related to SAF.
.02 Generally applicable definitions.
(1) Applicable material. Section 45Z(d)(5)(B)(i) defines the term “applicable
material” to mean (I) monoglycerides, diglycerides, and triglycerides, (II) free fatty acids,
and (III) fatty acid esters.
(2) ASTM or ASTM International. References in this notice to “ASTM” or “ASTM

-5International” are references to specifications published by ASTM International (formerly
ASTM). Additional information about ASTM International is available at
https://www.astm.org.
(3) Biomass. Section 45Z(d)(5)(B)(ii) gives the term “biomass” the same
meaning given such term in § 45K(c)(3). Section 45K(c)(3) defines the term “biomass”
to mean any organic material other than (A) oil and natural gas (or any product thereof),
and (B) coal (including lignite) or any product thereof.
(4) CO2e. Section 45Z(d)(2) defines the term “CO2e” to mean, with respect to
any greenhouse gas, the equivalent carbon dioxide (as determined based on relative
global warming potential).
(5) Greenhouse gas. Section 45Z(d)(3) gives the term “greenhouse gas” the
same meaning given that term under section 211(o)(1)(G) of the CAA, as in effect on
August 16, 2022.
(6) mmBTU. Section 45Z(d)(1) defines the term “mmBTU” to mean 1,000,000
British thermal units.
(7) Qualified facility. Under § 45Z(d)(4), the term “qualified facility” means a
facility used for the production of transportation fuels, and does not include any facility
for which one of the following credits is allowed under § 38 for the taxable year: (i) the
credit for production of clean hydrogen under § 45V, (ii) the credit determined under
§ 46 to the extent that such credit is attributable to the energy credit determined under
§ 48 with respect to any specified clean hydrogen production facility for which an
election is made under § 48(a)(15), and (iii) the credit for carbon oxide sequestration
under § 45Q.

-6(8) Sale. Under § 45Z(a)(1)(A)(ii) and (a)(4), a sale for purposes of the § 45Z
credit occurs when the transportation fuel is sold by the taxpayer to an unrelated person
(A) for use by such person in the production of a fuel mixture, (B) for use by such
person in a trade or business, or (C) who sells such fuel at retail to another person and
places such fuel in the fuel tank of such other person.
(9) Transportation fuel. Section 45Z(d)(5)(A) defines the term “transportation
fuel” to mean a fuel which (i) is suitable for use in a highway vehicle or aircraft, (ii) has
an emissions rate which is not greater than 50 kilograms of CO2e per mmBTU, and (iii)
is not derived from co-processing an applicable material (or materials derived from an
applicable material) with a feedstock which is not biomass. The term “transportation
fuel” includes non-SAF transportation fuel and SAF.
.03 Definitions applicable to non-SAF transportation fuels.
(1) Low-GHG biodiesel. The term “low-GHG biodiesel” means the monoalkyl
esters of long chain fatty acids that meet the specifications of ASTM International
D6751 and that have an emissions rate that is not greater than 50 kg of CO2e per
mmBTU.
(2) Low-GHG butanol. The term “low-GHG butanol” means any mixture of nbutyl, sec-butyl, and iso-butyl alcohols that meets the specifications of ASTM
International D7862 and that has an emissions rate that is not greater than 50 kg of
CO2e per mmBTU.
(3) Low-GHG diesel fuel. The term “low-GHG diesel fuel” means liquid fuel,
including renewable diesel, that meets the specifications of ASTM International D975
and that has an emissions rate that is not greater than 50 kg of CO2e per mmBTU.

-7(4) Low-GHG dimethyl ether. The term “low-GHG dimethyl ether,” which
includes renewable dimethyl ether, means a gaseous fuel that meets the specifications
of ASTM International D7901 and that has an emissions rate that is not greater than 50
kg of CO2e per mmBTU.
(5) Low-GHG ethanol. The term “low-GHG ethanol” means ethyl alcohol that is a
liquid fuel that meets the specifications of ASTM International D4806 for denatured fuel
ethanol for blending with gasolines and that has an emissions rate that is not greater
than 50 kg of CO2e per mmBTU.
(6) Low-GHG gasoline. The term “low-GHG gasoline,” which includes renewable
gasoline, means liquid fuel that meets the specifications of ASTM International D4814
and has an emissions rate that is not greater than 50 kg of CO2e per mmBTU.
(7) Low-GHG hydrogen. The term “low-GHG hydrogen” means any gaseous or
liquid fuel that meets the requirements of the Society of Automotive Engineers (SAE)
J2719 standard and that has an emissions rate that is not greater than 50 kg of CO2e
per mmBTU. Information about SAE standards is available at
https://www.sae.org/standards.
(8) Low-GHG liquefied petroleum gas (LPG). The term “low-GHG LPG,” which
includes low-GHG propane, means low-GHG liquefied gases that meet the
specifications of ASTM International D1835 and that has an emissions rate that is not
greater than 50 kg of CO2e per mmBTU.
(9) Low-GHG methanol. The term “low-GHG methanol” means a methyl alcohol
that is a liquid fuel that meets the specifications of ASTM International D5797 and that
has an emissions rate that is not greater than 50 kg of CO2e per mmBTU.

-8(10) Low-GHG natural gas. The term “low-GHG natural gas,” which includes
renewable natural gas, means compressed or liquefied gas that meets the
specifications of ASTM International D8080-21 and that has an emissions rate that is
not greater than 50 kg of CO2e per mmBTU.
.04 Definitions applicable to SAF.
(1) General definitions.
(a) SAF or sustainable aviation fuel. Section 45Z(a)(3)(B) defines the term
“sustainable aviation fuel” to mean the portion of liquid fuel that is not kerosene that is
sold for use in an aircraft and (i) meets the requirements of either (I) ASTM International
D7566 (further defined in section 3.04(2)(a) of this notice to mean the ASTM D7566
Annexes), or (II) the Fischer Tropsch provisions of ASTM D1655 Annex A1 (further
defined in section 3.04(2)(b) of this notice to mean ASTM D1655 Annex A1 section
A1.2.2.2); and (ii) is not derived from palm fatty acid distillates or petroleum. For
purposes of the § 45Z credit, SAF is a type of transportation fuel that must also meet
the requirements of § 45Z(d)(5)(A). A liquid fuel that meets the specifications of one of
the ASTM D7566 Annexes or meets the specifications of ASTM D1655 Annex A1, but
does not meet the requirements of § 45Z(d)(5)(A), is not SAF and is therefore ineligible
for the § 45Z credit.
For purposes of the § 45Z credit, SAF may be categorized as either (A) a liquid
fuel that meets the specifications of one of the ASTM D7566 Annexes (SAF synthetic
blending component), or (B) a co-processed liquid fuel that was produced by coprocessing petroleum with synthesized hydrocarbons derived from synthesis gas via the
Fischer Tropsch process (FT hydrocarbons).

-9(b) SAF FT hydrocarbons. The term “SAF FT hydrocarbons” means the FT
hydrocarbons that are derived from biomass, used to produce jet fuel described in
section A1.2.2.2 of ASTM D1655 Annex A1, and not derived from palm fatty acid
distillates or petroleum. See section 3.04(2)(b) of this notice.
(2) Definitions related to ASTM International specifications for SAF.
(a) ASTM D7566 Annexes. The term “ASTM D7566 Annexes” means any of the
annexes in ASTM D7566 that provide the specifications for a pathway to create a
synthetic blending component that can be blended with ASTM D1655 kerosene (as
defined in section 3.04(2)(c) of this notice).
(b) ASTM D1655 Annex A1. The term “ASTM D1655 Annex A1” means the
Fischer Tropsch provisions of ASTM D1655 Annex A1 that are contained in section
A1.2.2.2, which provides a pathway for co-processing up to five percent of FT
hydrocarbons with petroleum to make a liquid fuel that qualifies as jet fuel. For
purposes of this definition, the term “petroleum” includes any conventionally sourced
hydrocarbons permitted under ASTM D1655 Annex A1.
Liquid fuel produced under section A1.2.2.1 does not qualify for the § 45Z credit
because section A1.2.2.1 defines a pathway for producing a liquid fuel from coprocessing an applicable material (or materials derived from an applicable material) with
a feedstock that is not biomass (for example, petroleum), which § 45Z(d)(5)(A)(iii)
excludes from the § 45Z credit. See section 3.02 of this notice.
(c) ASTM D1655 kerosene and ASTM D1655 compliant SAF. The term “ASTM
D1655 kerosene” means petroleum-based kerosene that meets the specifications set
forth in ASTM D1655 and does not include liquid fuel co-processed with FT

- 10 hydrocarbons or the addition of a SAF synthetic blending component.
The term “ASTM D1655 compliant SAF” means ASTM D1655 kerosene that has
been blended with a SAF synthetic blending component described in a specific ASTM
D7566 Annex and meets the batch specifications described in ASTM D7566, Table 1. It
also means kerosene produced by co-processing SAF FT hydrocarbons with petroleum
under ASTM D1655 Annex A1. Once the mixture meets those batch specifications or is
produced under ASTM D1655 Annex A1, the mixture may be regarded as jet fuel under
ASTM D1655. ASTM D1655 compliant SAF is fully fungible with ASTM D1655
kerosene.
The terms “ASTM D1655 kerosene” and “ASTM D1655 compliant SAF” are not
ASTM designations, but rather are used in this notice to distinguish between two types
of fuel (for federal tax purposes) that qualify as jet fuel under the ASTM D1655
specifications for jet fuel.
(d) ASTM International D7566. The term “ASTM International D7566” means the
batch specifications set forth under ASTM D7566, Table 1, which includes the blending
requirements for each synthetic blending component and the overall specifications and
requirements for the blended mixture to be regarded as ASTM D1655 compliant SAF.
Blending percentage requirements for various synthetic blending components with
ASTM D1655 kerosene are listed in section 6 of ASTM D7566 and range from 10 to 50
percent.

- 11 SECTION 4. REGISTRATION AS A PRODUCER OF CLEAN FUEL
.01 Registration generally.
(1) Statutory registration requirement. Section 45Z(f)(1)(A)(i)(l) provides that no
clean fuel production credit can be determined under § 45Z(a) with respect to any
transportation fuel unless the taxpayer is registered as a producer of clean fuel under
§ 4101 at the time of production. 4 See § 48.4101-1 of the Manufacturers and Retailers
Excise Tax Regulations for rules relating to registration under § 4101. 5
(2) Registration letter; timing of applications for registration. A person is
registered for purposes of § 45Z(f)(1)(A)(i)(l) only if the IRS has issued a registration
letter to the person and the registration has not been revoked or suspended. To be
eligible to claim the § 45Z credit for production starting January 1, 2025, a taxpayer
must have a signed registration letter dated on or before January 1, 2025. For example,
if a taxpayer receives a letter of registration dated June 30, 2025, the taxpayer cannot
claim the § 45Z credit for any transportation fuel produced and sold by the taxpayer
before June 30, 2025, even if all other statutory requirements for the § 45Z credit are
satisfied prior to that date. That taxpayer can only claim the § 45Z credit for
transportation fuel produced and sold on or after June 30, 2025.

Section 45Z(f)(1)(A)(i)(I) provides that “[n]o clean fuel production credit shall be determined under
[§ 45Z](a) with respect to any transportation fuel unless the taxpayer is registered as a producer of clean
fuel under § 4101 at the time of production,…”. Section 13704(b)(5) of the IRA provided that for
transportation fuel produced after December 31, 2024, "Section 4101(a)(1), as amended by the preceding
provisions of this Act, is amended by inserting the phrase ‘every person producing a fuel eligible for the
clean fuel production credit (pursuant to section 45Z)’ after ‘section 6426(k)(3)).’” However, § 4101(a)(1)
does not reference § 6426(k)(3). The Office of Law Revision Counsel of the U.S. House of
Representatives, whose functions include preparing and publishing periodically a new edition of the
United States Code, executed the provision by making the insertion after "section 40B)," to reflect the
probable intent of Congress.
5 The Treasury Department and the IRS intend to update the regulations under § 4101 to reflect the
registration requirement in § 45Z(f)(1)(A)(i)(I).
4

- 12 Given the requirement that a taxpayer must be registered at the time of
production to claim the § 45Z credit, taxpayers are encouraged to apply for registration
as soon as possible to give the IRS sufficient time to process registration applications
for the § 45Z credit. The IRS intends to process completed applications for registration
received by July 15, 2024, such that an eligible taxpayer can receive its letter of
registration by January 1, 2025. The IRS intends to quickly process applications
received after July 15, 2024, but cautions that a taxpayer that applies for registration
after that date is less likely to receive its registration by January 1, 2025. In no event
can the IRS guarantee that any application for registration will be processed by a certain
date.
(3) Effect of registration letter. Registration is one of the requirements for a
taxpayer to be eligible to claim the § 45Z credit. The taxpayer and the fuel(s) that the
taxpayer produces must also meet the other § 45Z requirements for the taxpayer to be
eligible to claim the § 45Z credit. A registration letter is not a determination by the IRS
that the registrant may claim the § 45Z credit. For example, a registration for Activity
Letter “CN” issued to a taxpayer producing biodiesel is not a determination that the
biodiesel meets the definition of transportation fuel under § 45Z(d)(5) or that the facility
where the taxpayer produces such biodiesel meets the definition of a qualified facility
under § 45Z(d)(4).
(4) Procedures and information for registering generally. Application for
registration is made on Form 637, “Application for Registration (for Certain Excise Tax
Activities),” under Activity Letter “CN” (for a producer of non-SAF transportation fuel), or
Activity Letter “CA” (for a producer of SAF), or both, in accordance with the instructions

- 13 for that form. The IRS is revising Form 637 to add Activity Letters “CN” and “CA.” An
applicant may apply for registration under more than one Activity Letter on a single
Form 637.
Until the revised Form 637 is released, applicants may use the current Form 637
by writing in Activity Letter “CN” or Activity Letter “CA,” or both, as applicable, and
providing the corresponding information required by section 4.02 and 4.03 of this notice.
(5) Transportation fuel; feedstocks; co-processor registration. The information in
this section 4.01(5) and Appendix A is provided solely for purposes of applications for
registration and is not determinative of whether a fuel is transportation fuel.
Qualification of a fuel as transportation fuel depends on the specific facts and
circumstances, including the emissions rate of such fuel.
(A) Non-SAF transportation fuel. In consultation with the Department of Energy
(DOE), the Treasury Department and the IRS anticipate that low-GHG biodiesel, lowGHG butanol, low-GHG diesel fuel, low-GHG dimethyl ether, low-GHG ethanol, lowGHG gasoline, low-GHG hydrogen, low-GHG LPG, low-GHG methanol, and low-GHG
natural gas may qualify as non-SAF transportation fuel taking into consideration the
emissions rate threshold in § 45Z(d)(5)(A)(ii). See section 3.03 of this notice for
definitions of these types of fuel. Most fuels derived from palm fatty acid distillates,
petroleum, natural gas, and coal (including lignite) are not expected to qualify as nonSAF transportation fuel based on the § 45Z(d)(5)(A)(ii) emissions rate threshold. A
producer of non-SAF transportation fuel not defined in section 3.03 of this notice should
submit an application for registration if such producer anticipates such fuel to be eligible
for the § 45Z credit.

- 14 (B) Co-processed SAF. For SAF produced by co-processing petroleum with SAF
FT hydrocarbons, the co-processor is the party that applies for registration under this
notice.
(C) Feedstocks used to produce transportation fuel; additional fuels and
feedstocks. In Appendix A, the Treasury Department and the IRS, in consultation with
the DOE, have identified the feedstocks and feedstock types associated with the
varieties of fuel that may qualify as transportation fuel. The Treasury Department and
the IRS may provide guidance at a later time about additional fuels (and the feedstocks
for such fuels) that may be eligible for the § 45Z credit.
.02 Registration procedure and requirements for producers of non-SAF
transportation fuel eligible for the § 45Z credit.
(1) Procedure for registering. Until the revised Form 637 is released, applicants
producing non-SAF transportation fuel eligible for the § 45Z credit may use the current
Form 637 by writing in Activity Letter “CN” and providing the following information:
(A) Each type of non-SAF transportation fuel and the annual volume of each type
of non-SAF transportation fuel the applicant produces. If a type of non-SAF
transportation fuel the applicant produces is not described in section 4.01(5)(A) of this
notice, state “Other” and provide a description of the fuel;
(B) The feedstock(s) and country of origin of each feedstock used to produce
each type of non-SAF transportation fuel the applicant produces;
(C) The location(s) and a description of the applicant’s production facilities;
(D) Each production facility’s annual fuel production capacity, and whether the
applicant’s production facilities are operational and currently producing volumes of non-

- 15 SAF transportation fuel;
(E) The names and addresses of any person(s) acting for the applicant as an
agent or broker in buying, selling, or transporting any non-SAF transportation fuel;
(F) The business entities to which the applicant sells non-SAF transportation fuel;
(G) The business entities from or with which the applicant buys, trades, transfers,
or exchanges any non-SAF transportation fuel;
(H) The annual volume of non-SAF transportation fuel the applicant buys, sells,
trades, transfers, or exchanges; and
(I) A statement indicating under which ASTM standard(s), SAE standard(s), or
both, the applicant produces non-SAF transportation fuel.
(2) Requirements. The IRS will register an applicant with Activity Letter “CN”
only if the IRS (A) concludes that the applicant is engaged as a producer of non-SAF
transportation fuel that may be eligible for the § 45Z credit, or is likely to become so
engaged within a reasonable time after being registered; and (B) is satisfied with the
filing, deposit, payment, reporting, and claim history for all federal taxes of the applicant
and any related person (as defined in § 48.4101-1(b)(5)).
.03 Registration procedure and requirements for producers of SAF eligible for the
§ 45Z credit.
(1) Procedure for registering. Until the revised Form 637 is released, applicants
producing SAF eligible for the § 45Z credit may use the current Form 637 by writing in
Activity Letter “CA” and providing the following information:
(A) A statement indicating whether the applicant produces SAF under an ASTM
D7566 Annex or ASTM D1655 Annex A1, and if applicable, the specific ASTM D7566

- 16 Annex under which the SAF synthetic blending component is produced;
(B) The feedstock(s) and country of origin of each feedstock used to produce the
SAF the applicant produces;
(C) The annual volume of SAF the applicant produces;
(D) The location(s) and a description of the applicant’s production facilities;
(E) Each production facility’s annual fuel production capacity, and whether the
applicant’s production facilities are operational and currently producing volumes of SAF;
(F) The names and addresses of any person(s) acting for the applicant as an
agent or broker in buying, selling, or transporting any SAF;
(G) The business entities to which the applicant sells SAF;
(H) The business entities from or with which the applicant buys, trades, transfers,
or exchanges any SAF; and
(I) The annual volume of SAF the applicant buys, sells, trades, transfers, or
exchanges.
(2) Requirements. The IRS will register an applicant with Activity Letter “CA” only
if the IRS (A) concludes that the applicant is engaged as a producer of SAF that may be
eligible for the § 45Z credit, or is likely to become so engaged within a reasonable time
after becoming registered; and (B) is satisfied with the filing, deposit, payment,
reporting, and claim history for all federal taxes of the applicant and any related person
(as defined in § 48.4101-1(b)(5)).
SECTION 5. INFORMATION ABOUT OTHER FUEL REGISTRATIONS
Section 4101(a)(1) requires that every person required to be registered with
respect to the tax imposed by § 4041(a) or 4081, every person producing or importing

- 17 biodiesel (as defined in § 40A(d)(1) including agri-biodiesel and renewable diesel) or
alcohol (as defined in § 6426(b)(4)(A)), every person producing or importing sustainable
aviation fuel (as defined in § 40B), and every person producing second generation
biofuel (as defined in § 40(b)(6)(E)), register under § 4101.
Section 4081(a)(1) imposes an excise tax on certain removals, entries, and sales
of taxable fuel. Section 4083(a) defines taxable fuel as gasoline, diesel fuel, and
kerosene. Section 4041(a) imposes an excise tax on certain sales and uses of diesel
fuel and kerosene.
Depending on the type of transportation fuel being produced and sold, a person
producing fuel eligible for the § 45Z credit may have additional registration obligations
under § 4101 and § 48.4101-1 and thus may be required to be registered under other
activity letters (in addition to Activity Letters “CN” and/or “CA”), including the following:
(A) Activity Letter “SA” (producers or importers of sustainable aviation fuel as
defined in § 40B);
(B) Activity Letter “S” (enterer, position holder, refiner, terminal operator, or
throughputter of gasoline, diesel fuel (including a diesel-water fuel emulsion), or
kerosene, or industrial user of gasoline);
(C) Activity Letter “M” (blenders of gasoline, diesel fuel (including a diesel-water
fuel emulsion) or kerosene, producing a taxable fuel outside the bulk transfer/terminal
system, including blenders of alcohol fuel mixtures, alternative fuel mixtures, biodiesel
mixtures, and renewable diesel mixtures);
(D) Activity Letter “AB” (producers and importers of agri-biodiesel);
(E) Activity Letter “AF” (producers and importers of alcohol);

- 18 (F) Activity Letter “NB” (producers and importers of biodiesel (other than agribiodiesel) and renewable diesel); and
(G) Activity Letter “SB” (producers of second generation biofuel).
If a person is producing SAF eligible for the § 45Z credit and that SAF also meets
the definition of sustainable aviation fuel under § 40B, such person must also be
registered under Activity Letter “SA”. 6
For additional guidance for fuel registrations, see Notice 2023-6 (guidance on
sustainable aviation fuel credits under §§ 40B and 6426(k)), Notice 2008-110, 2008-51
I.R.B. 1298 (guidance on biodiesel and registration for the cellulosic biofuel producer
credit), 7 and Notice 2005-4, 2005-2 I.R.B. 289 (guidance on alcohol and biodiesel fuel
tax credits and payments), as modified by Notice 2005-62, 2005-35 I.R.B. 443
(guidance for certain biodiesel issues not addressed in Notice 2005-4).
SECTION 6. PAPERWORK REDUCTION ACT
Section 4 of this notice sets forth collections of information to be provided to the
IRS with Form 637. The collections of information will be reflected in the submission to
the Office of Management and Budget (OMB) for review in accordance with the
Paperwork Reduction Act (44 U.S.C. 3507(c)) that is associated with Form 637 (OMB
control number 1545-1835). The revisions to Form 637 and the new activity letters to
be submitted with Form 637, outlined in section 4 of this notice, will be submitted to

Section 40B(d) and § 45Z(b)(1)(B)(ii) define SAF in identical terms. However, the formulas used to
qualify for and calculate the respective credits according to emissions are different. See Notice 2023-6,
2023-2 I.R.B. 328, Notice 2024-6, 2024-2 I.R.B. 348, and Notice 2024-37, 2024-21 I.R.B. 1191, for
additional information regarding § 40B.
7 Section 404 of the American Taxpayer Relief Act of 2012, Public Law 112-240, 126 Stat. 2313 (January
2, 2013), modified and extended what was previously known as the cellulosic biofuel producer credit of
§ 40(b)(6), replacing the term “cellulosic biofuel” with “second generation biofuel” and expanding the list of
qualifying feedstocks to include algae.
6

- 19 OMB for review and approval under the PRA procedures within 5 CFR 1320.10. An
agency may not conduct or sponsor, and a person is not required to respond to, a
collection of information unless the collection of information displays a valid OMB
control number.
SECTION 7. DRAFTING INFORMATION
The principal authors of this notice are Camille Edwards Bennehoff and Jennifer
Golden of the Office of Associate Chief Counsel (Passthroughs & Special Industries).
For questions regarding this notice, contact Ms. Edwards Bennehoff or Ms. Golden at
(202) 317-6855 (not a toll-free number).

Appendix A – Table of Feedstocks* Used to Make
Fuels that May Be Eligible for the § 45Z Credit
*

Appendix A identifies primary feedstocks used to make transportation fuels that may
be eligible for the § 45Z credit for purposes of applications for registration.
Producers should list the feedstock(s) that are sourced from one or more separate
entities or facilities as the main input(s) to their fuel production process. For
example, an alcohol-to-jet (ATJ) producer that imports ethanol from one or more
separate ethanol production facilities may list ethanol as the feedstock, whereas an
integrated ATJ facility with on-site ethanol production should list the feedstock used
to produce the ethanol. Renewable natural gas (RNG) producers with on-site
anaerobic digestion should list the inputs to the digester (for example, manure or
food waste) as feedstocks, whereas RNG producers that import biogas from a
separate site should list biogas as the feedstock.

** For purposes of Appendix A, “dedicated” means woody biomass grown for the
purpose of being harvested for biofuel production.
Feedstock Type

Feedstock

Agricultural Residue

Barley straw

Agricultural Residue

Corn stover

Agricultural Residue

Cotton field residues

Agricultural Residue

Oats straw

Agricultural Residue

Orchard or vineyard
residues

Agricultural Residue

Rice straw

Agricultural Residue

Sorghum stubble

Agricultural Residue

Sugarcane bagasse

Agricultural Residue

Wheat straw

Agricultural Residue

Other agricultural
residues

Additional Information

-2Feedstock Type

Feedstock

Algae

Algal oil

Biogas

Dairy/swine digester gas

Biogas

High solid anaerobic

Additional Information

digester gas
Biogas

Landfill gas

Biogas

Waste gases

Biogas

Other biomethane

Biomass Energy Crop

Biomass sorghum

Biomass Energy Crop

Energy cane

Biomass Energy Crop

Miscanthus

Biomass Energy Crop

Switchgrass

Biomass Energy Crop

Other biomass energy
crop

CO2

CO2 co-produced with

Includes CO2 co-produced with hydrogen

hydrogen

produced for use in the Haber-Bosch
process

CO2

CO2 from biogas

Includes CO2 from landfill gas upgrading

upgrading
CO2

CO2 from calcination of
inorganic materials in
cement production

CO2

CO2 from direct air
capture

CO2

CO2 from ethanol
fermentation

CO2

CO2 from ore oxidation in
iron and steel production

CO2

Post-combustion

Includes only CO2 captured from

captured biogenic CO2

combustion of bio-based materials (for
example, biomass, biogas)

CO2

Post-combustion

Includes only CO2 captured from

captured fossil CO2

combustion of fossil fuels

CO2

Other CO2 source

Ethanol

Corn grain

Applicable for SAF only

Ethanol

Sugarcane

Applicable for SAF only

-3Feedstock Type

Feedstock

Additional Information

Ethanol

Other sugar crop

Applicable for SAF only

Ethanol

Other grain crop

Applicable for SAF only

Ethanol

Other feedstocks

Applicable for SAF only

Fats, Oils, and Greases

Tallow

Fats, Oils, and Greases

Tall oil

Fats, Oils, and Greases

Used cooking oil

Fats, Oils, and Greases

Tallow

Industrial Byproduct

Black liquor

Industrial Byproduct

Corn kernel fiber

Industrial Byproduct

Distillers corn oil

Industrial Byproduct

Distillers sorghum oil

Industrial Byproduct

Milling residues

Industrial Byproduct

Nut hulls or shells

Industrial Byproduct

Other byproduct

Industrial Byproduct

Other food or beverage

This includes brewery, winery, and

manufacturing wastes

distillery waste, including spent grain

Isobutanol

Corn grain

Applicable for SAF only

Isobutanol

Sugarcane

Applicable for SAF only

Isobutanol

Other feedstocks

Applicable for SAF only

Isobutanol

Other grain crop

Applicable for SAF only

Isobutanol

Other sugar crop

Applicable for SAF only

Manure

Manure, beef

Manure

Manure, dairy

Manure

Manure, swine

Mixed Organic Waste

Construction, demolition,
or other urban wood
waste

Mixed Organic Waste

Mixed non-residential
food waste

Mixed Organic Waste

Mixed residential food
waste

Mixed Organic Waste

Municipal solid waste

Mixed Organic Waste

Paper and paperboard
Wastewater treatment

Mixed Organic Waste

Sludge

-4Feedstock Type

Feedstock

Mixed Organic Waste

Yard waste

Mixed Organic Waste

Other mixed organic

Additional Information

waste
Natural Gas

Natural gas

Natural Gas

Renewable natural gas

Oilseed

Jatropha oil

Oilseed

Palm oil

Potentially eligible feedstock for non-SAF
transportation fuel. SAF derived from palm
fatty acid distillates is explicitly prohibited

Oilseed

Rapeseed/canola oil

Oilseed

Soybean oil

Oilseed

Other oilseed

Other Alcohols

Corn grain

Applicable for SAF only

Other Alcohols

Sugarcane

Applicable for SAF only

Other Alcohols

Other feedstocks

Applicable for SAF only

Other Alcohols

Other grain crop

Applicable for SAF only

Other Alcohols

Other sugar crop

Applicable for SAF only

Second or Intermediate Crop

Camelina

Second or Intermediate Crop

Carinata

Second or Intermediate Crop

Corn safrina

Second or Intermediate Crop

Other second or
intermediate crop

Second or Intermediate Crop

Pennycress

Starch Crop

Barley

Starch Crop

Corn grain

Starch Crop

Grain sorghum

Starch Crop

Wheat

Starch Crop

Other starch crop

Sugar Crop

Sugarbeet

Sugar Crop

Sugarcane

Sugar Crop

Sweet sorghum

Sugar Crop

Other sugar crop

Woody Biomass

Forest slash

Woody Biomass

Pre-commercial thinnings

-5Feedstock Type

Feedstock

Woody Biomass

Dedicated short-rotation

Additional Information

poplar**
Woody Biomass

Dedicated short-rotation
willow**

Woody Biomass

Dedicated pine**

Woody Biomass

Dedicated short-rotation
eucalyptus**

Woody Biomass

Other dedicated woody
Biomass**

Woody Biomass

Other woody biomass
residues

Other

A feedstock used to

On your Form 637, state “Other” and

produce a fuel eligible for

provide a description of the feedstock

the § 45Z credit which is
not listed in this table