IRS Form 637 is the federal registration a fuel business needs before it can produce, blend, or sell certain fuels, and before it can claim most fuel excise tax credits. You register for specific activities, each tagged with a one or two letter code, and the IRS issues a Letter of Registration once it approves you. The rule that trips up jobbers is timing. The registration has to be approved before you claim the credit, not filed alongside it.
What Form 637 actually is
The full title is Application for Registration (For Certain Excise Tax Activities). It exists because Internal Revenue Code section 4101 requires certain people in the fuel chain to register with the IRS before they carry out taxable or credit-generating activities. Once approved, you get a Letter of Registration with a registration number, and that number is what you reference when you file your excise returns and claims on Form 720 and Form 8849.
You do not register one time for everything you might ever do. You register for the specific activities you actually perform, and each activity has its own letter code. A business that blends biodiesel and also sells undyed diesel to farms carries two codes on one registration.
Who has to register
The registration net covers producers and importers of taxable fuel, blenders, terminal operators, position holders, ultimate vendors that claim credits on tax-paid fuel, and alternative fuelers. A jobber who only buys tax-paid product from a rack and resells it, collecting nothing back from the IRS, often does not need a 637 at all. The moment you start blending your own product, or you want to claim a credit on fuel that ended up in an exempt use, registration becomes the gate you have to pass through first.
The activity letters a fuel business runs into
There are dozens of activity letters on Form 637, most of which never touch a jobber. These are the ones that do:
- Code S, ultimate vendor of undyed diesel and undyed kerosene. Covers selling clear, tax-paid diesel or kerosene for use on a farm for farming, or to a state or local government, or undyed kerosene from a blocked pump. This is the code a jobber needs to claim the ultimate vendor credit on those sales.
- Code M, blender. A person who produces a blended taxable fuel outside the terminal, including blending biodiesel into diesel to make a biodiesel mixture. If you splash biodiesel and want the mixture treated correctly, this is your code.
- Codes UV and UP, other ultimate vendor codes. These cover exempt sales beyond the farm and government cases, such as undyed diesel or kerosene sold to certain bus operators and kerosene sold for use in aviation. The Form 637 instructions spell out which letter maps to which sale, so match the letter to the exact type of sale you make.
- Code AL, alternative fueler. For selling or delivering alternative fuel such as propane, LNG, or CNG into a vehicle or motorboat tank, using it in your own business, or producing an alternative fuel mixture. If you run an LP-gas motor fuel operation, this is the one to look at.
- Others you may see. A (producer or importer of taxable fuel), C (certain gasoline blendstock sales), and K (kerosene feedstock buyers) show up in larger operations. Most jobbers never file these.
Note that dyed diesel does not run through the ultimate vendor credit system, because it is sold without the federal tax in the first place. If most of your off-road volume moves as red fuel, read how dyed diesel is taxed before you assume you need an S registration.
Worked example: blending biodiesel and selling undyed diesel to a farm
Say you run a mid-size jobber operation. You buy B100 biodiesel, blend it with ULSD at your bulk plant to make a B20, and you also deliver clear, tax-paid diesel to a row-crop farm down the road. Two different activities, two different codes.
The blending is a producer activity. To have your biodiesel mixture treated correctly for federal excise purposes, you register under M as a blender. Historically the biodiesel mixture credit was worth one dollar per gallon of biodiesel under code section 6426, and it always required the claimant to be registered. That excise credit lapsed at the end of 2024, and Congress moved the support into the clean fuel production credit under section 45Z for later years, which carries its own registration. The registration discipline did not go away. If you are also generating and separating RINs on that blend, the Renewable Fuel Standard is a separate program with its own EPA registration on top of the IRS side.
The farm delivery is the ultimate vendor case. The farmer is putting clear diesel into off-road farm use, which is a nontaxable use, so the roughly 24.3 cents a gallon of federal diesel tax baked into that fuel can be recovered. Either the farmer claims it, or you claim it as the ultimate vendor, but you can only file that claim if you hold an S registration and you have the required certificate or waiver from the farm on file. The farm exemption itself is covered in fuel tax exemptions. Form 637 is what turns that exemption into money you can actually claim back.
You cannot claim the credit until the registration is approved
This is the part that costs people real money. Registration is not automatic and it is not instant. After you file Form 637, the IRS reviews the application, may run a background and financial check, and can send an agent to inspect your premises and records before it approves you. That process can run several months. Until the Letter of Registration is in your hand, you are not registered, and a credit claim filed by an unregistered vendor gets denied. If you wait until you have a pile of qualifying gallons to apply, you have already lost the ones that came before approval.
Registration does not expire on a calendar, but the IRS can revoke or suspend it if you stop meeting the requirements or you stop filing. You also have to notify the IRS when your business facts change, such as a new owner, a new location, or dropping an activity.
How to apply and keep it clean
File Form 637 with the activity letters you need, answer the ownership and facilities questions honestly, and expect the IRS to verify what you claimed. Some activities also require a bond, which sits in the same family as the state-level guarantees covered in motor fuel tax bonds. After approval, the work is record keeping. You have to be able to show, gallon for gallon, which fuel qualified for which credit, and tie every claim back to a certificate, a delivery ticket, and your registration number.
That reconciliation is where a lot of jobbers leak money, because the qualifying gallons are scattered across blend tickets, farm deliveries, and cardlock pulls that live in different places. A back office system that tags each load with its tax treatment as it moves, the way FastDragon is built to, is what keeps a 637 claim defensible when the IRS asks you to prove it. Whatever you use, do not run this out of a shoebox.
One 637 does not replace your state fuel licenses. It is a federal registration, and every state you haul in has its own separate motor fuel registration and reporting. Treat the two tracks as parallel, not one covering the other.
Questions people ask
How long does IRS approval of Form 637 usually take?
Plan for several months, not weeks. The IRS reviews the application, can run financial and background checks, and may inspect your facilities before issuing the Letter of Registration. File well ahead of when you expect to need the registration active.
Does a 637 registration have to be renewed each year?
There is no annual renewal date. The registration stays in force until the IRS revokes or suspends it, which it can do if you stop filing, stop meeting the activity requirements, or fail to report a change such as new ownership or a new location.
Where does my registration number go once I have it?
You reference it on your federal excise filings, mainly Form 720 and the Form 8849 refund and Schedule 3 credit claims tied to your activities. The number is how the IRS matches a claim to an approved registrant.
Do I still need state fuel tax licenses if I have a 637?
Yes. Form 637 is federal only. Every state where you produce, blend, sell, or haul fuel runs its own registration and reporting, and those obligations are entirely separate from your IRS registration.