IFTA Reporting for Mixed Fleets: Diesel, Gasoline, and Alternative Fuels

If your fleet runs anything other than straight diesel, IFTA reporting gets more complicated. Gasoline-powered trucks, compressed natural gas (CNG) vehicles, liquefied natural gas (LNG) tractors, propane-fueled equipment, and ethanol blends all have different tax rates, different MPG expectations, and different reporting requirements under IFTA. Mixing fuel types in a single fleet means filing separate calculations for each fuel type — and getting the details wrong can trigger audit inquiries or result in overpaying taxes.

This guide covers how IFTA handles multiple fuel types, the reporting structure for mixed fleets, how tax rates differ by fuel, and the practical steps to file accurately when your vehicles don't all burn the same thing.

In this guide, you will learn:

• Which fuel types IFTA recognizes and how they're classified
• How tax rates differ by fuel type across states
• The difference between Schedule 1 and Schedule 2 reporting
• How to calculate MPG for different fuel types
• Practical filing steps for mixed-fuel fleets

IFTA Fuel Type Classifications

IFTA recognizes several fuel types, each with its own tax rate schedule. The primary classifications are:

• Diesel (D): Standard #2 diesel fuel, including ultra-low sulfur diesel (ULSD). This is the most common fuel type for Class 8 vehicles.
• Gasoline (G): Regular, mid-grade, and premium gasoline. Used in some Class 6–7 trucks and certain specialty vehicles.
• Gasohol/Ethanol (A): Ethanol blends (E85 and similar). Some states tax ethanol differently from straight gasoline.
• Propane/LPG (P): Liquefied petroleum gas. Used in some fleet vehicles, particularly in urban delivery operations.
• CNG — Compressed Natural Gas (C): Increasingly common in regional haul and refuse operations.
• LNG — Liquefied Natural Gas (L): Used in some long-haul applications, though less common than CNG.
• Methanol (M): Rarely used in commercial trucking but recognized by IFTA.
• E-85 (E): 85% ethanol blend, classified separately from regular gasohol in some jurisdictions.
• Biodiesel (BD): Some jurisdictions classify biodiesel blends separately from standard diesel.
• Electricity (EL): An emerging category as electric commercial vehicles enter the market. Not all jurisdictions have established rates yet.

Each fuel type is identified by a code on the IFTA return. The fuel type code determines which rate table you reference when calculating tax owed per state. Using the wrong fuel type code is a common error that results in incorrect tax calculations.

How Tax Rates Differ by Fuel Type

State fuel tax rates are not uniform across fuel types. Most states tax diesel and gasoline at different rates, and alternative fuels often have their own rate structures. The differences can be significant.

Note that CNG and LNG rates in some states are dramatically lower than diesel, reflecting policy incentives for cleaner-burning fuels. California's CNG rate, for example, is roughly one-eighth of its diesel rate. This creates a meaningful fuel tax advantage for CNG-powered fleets operating in those states.

Also note the measurement units. CNG is typically measured in gasoline gallon equivalents (GGE)— the amount of CNG that has the same energy content as one gallon of gasoline. LNG may be measured indiesel gallon equivalents (DGE). These unit differences matter when you're calculating gallons consumed and MPG.

Schedule 1 vs. Schedule 2: IFTA Reporting Structure

When you file an IFTA return with multiple fuel types, you complete a separate schedule for each fuel type. The standard reporting structure:

• Schedule 1 (Tax Calculation): One Schedule 1 per fuel type. This is where you report miles by jurisdiction, calculate taxable gallons, apply fuel credits, and determine net tax owed per state. If you run diesel and gasoline vehicles, you complete two Schedule 1 forms — one for diesel operations and one for gasoline operations.
• Schedule 2 (Fuel Summary): A detailed listing of all fuel purchases for each fuel type. Schedule 2 supports the fuel credits claimed on Schedule 1. It lists each purchase with date, vendor, location, gallons, and cost.
• Summary Page: Combines the net tax from all Schedule 1 forms into a single total due or refund amount.

The critical point: each fuel type is calculated independently. You do not mix diesel miles with gasoline miles or combine their fuel purchases. Each fuel type has its own MPG, its own state mileage breakdown, and its own tax rates.

Calculating MPG for Different Fuel Types

MPG varies dramatically by fuel type. Diesel engines are more efficient per gallon than gasoline engines, and alternative fuels have their own efficiency profiles. When reporting multiple fuel types, you calculate separate MPG for each.

Gasoline-powered trucks get fewer miles per gallon than their diesel counterparts, but gasoline tax rates are often lower. The net tax effect depends on the specific rates in your operating states. Propane has the lowest MPG but also some of the lowest tax rates, creating an offsetting effect.

CNG and LNG Unit Conversions

CNG is sold by the GGE (gasoline gallon equivalent), and some states tax CNG per GGE. One GGE of CNG equals approximately 126.67 cubic feet or 5.66 pounds of natural gas. LNG is sold by the gallon but may be taxed per DGE (diesel gallon equivalent), where one DGE equals approximately 1.7 gallons of LNG.

These conversions matter for your MPG calculation. If your CNG truck consumes 3,000 GGE over 15,000 miles, its MPG is 15,000 ÷ 3,000 = 5.0 miles per GGE. That's the number you use on the IFTA return — not miles per cubic foot or any other unit.

Step-by-Step Filing for Mixed Fleets

Here is the process for filing an IFTA return when your fleet uses multiple fuel types:

Step 1: Separate Vehicles by Fuel Type

Group your fleet by fuel type. All diesel vehicles go in one group, all gasoline vehicles in another, CNG in a third, and so on. Each group will have its own Schedule 1.

Step 2: Calculate Miles by State for Each Fuel Group

Total the miles driven in each jurisdiction for each fuel type group. Your diesel trucks' Texas miles are separate from your gasoline trucks' Texas miles. Even if both types of trucks ran the same routes, the mileage is tracked and reported independently.

Step 3: Calculate MPG for Each Fuel Group

Compute fleet MPG separately for each fuel type:

• Diesel MPG = Total diesel vehicle miles ÷ total diesel gallons consumed
• Gasoline MPG = Total gasoline vehicle miles ÷ total gasoline gallons consumed
• CNG MPG = Total CNG vehicle miles ÷ total GGE consumed

Step 4: Complete a Schedule 1 for Each Fuel Type

For each fuel type, fill in the Schedule 1 with that group's miles per state, MPG, fuel purchased per state, and the corresponding tax rates from the fuel-type-specific rate table. The math is the same as a single-fuel return — you just repeat it for each fuel type.

Step 5: Complete Schedule 2 for Each Fuel Type

List all fuel purchases for each fuel type on a separate Schedule 2. A diesel receipt goes on the diesel Schedule 2. A CNG fill goes on the CNG Schedule 2. Do not combine receipts from different fuel types.

Step 6: Sum All Schedules on the Summary Page

The summary page totals the net tax (or credit) from each Schedule 1 into a single amount. You may owe tax on your diesel operations but receive a credit on your CNG operations, or vice versa. The summary page nets everything out into one payment or refund.

Common Mistakes in Multi-Fuel Reporting

Mixing Fuel Types on One Schedule

The most frequent error. A carrier with 8 diesel trucks and 2 gasoline trucks combines all miles and fuel on a single diesel Schedule 1. This applies diesel tax rates to gasoline consumption (or vice versa) and produces an incorrect MPG that reflects neither fuel type accurately.

Using Diesel Rates for Alternative Fuels

CNG, LNG, and propane have their own rate tables. Some states don't have published rates for every alternative fuel type, which requires contacting the jurisdiction directly. Defaulting to diesel rates overstates the tax liability for alternative fuels in most states.

Incorrect Unit Conversions for CNG/LNG

CNG stations may report fuel in therms, cubic feet, or GGE. Your IFTA return needs GGE (or the unit specified by the jurisdiction). If your receipts show cubic feet, you must convert to GGE before entering the data. One GGE = approximately 126.67 cubic feet of CNG.

Applying Fleet-Wide MPG Across Fuel Types

A fleet with diesel trucks at 6.0 MPG and gasoline trucks at 4.5 MPG cannot use a blended 5.5 MPG for the whole fleet. Each fuel type needs its own MPG. Blending them undercharges gasoline vehicles and overcharges diesel vehicles.

Forgetting to Report a Fuel Type

If you have one propane-powered vehicle in a fleet of 20 diesel trucks, it's easy to forget that the propane vehicle needs its own schedule. Every fuel type operated during the quarter must be reported.

Tax Advantages of Alternative Fuels Under IFTA

Some carriers specifically choose CNG or LNG partly because of the IFTA tax advantage. In states like California, where the diesel tax rate exceeds $0.70 per gallon but the CNG rate is under $0.09 per GGE, the fuel tax savings are substantial. A CNG truck burning 4,000 GGE per quarter in California owes roughly $355 in California fuel tax at the CNG rate, versus $2,824 for a comparable diesel truck burning 4,000 gallons — a difference of nearly $2,500 in a single state.

These tax incentives vary by state and can change quarterly. Some states are beginning to raise alternative fuel tax rates as adoption grows, narrowing the gap. But for now, CNG and LNG operations benefit from meaningfully lower IFTA tax burdens in many jurisdictions.

Electric Vehicles and IFTA

Battery-electric commercial vehicles are an emerging challenge for IFTA. Electricity isn't purchased at the pump the way diesel or CNG is, and many states haven't yet established IFTA tax rates for electricity. As of 2026, IFTA Inc. is working with member jurisdictions to develop a framework for taxing electric vehicle miles.

If you operate electric commercial vehicles interstate, check with your base jurisdiction for current guidance. Some states require electric CMVs to pay a flat per-mile fee in lieu of fuel tax. Others exempt them entirely (for now). The landscape is evolving, and carriers running mixed fleets that include EVs should stay informed as new policies emerge.

Frequently Asked Questions

Do I need a separate IFTA license for each fuel type?

No. Your IFTA license covers your entire fleet regardless of fuel types. You file a single quarterly return that includes separate schedules for each fuel type, but the license itself is fleet-wide.

What if a vehicle switches fuel types mid-quarter?

This is extremely rare (a vehicle would need a fuel system conversion), but if it happens, report the miles and fuel before the conversion under the original fuel type and the miles and fuel after the conversion under the new fuel type. Document the conversion date and the odometer reading at the time of the switch.

Can I use biodiesel without reporting it separately?

In most jurisdictions, standard biodiesel blends (B5, B20) are reported as diesel. Pure biodiesel (B100) may need to be reported separately in some states. Check your base jurisdiction's guidelines. If in doubt, report biodiesel blends as diesel unless your state specifically requires separate classification.

How do dual-fuel vehicles get reported?

Some vehicles can run on two fuel types (e.g., diesel and CNG in a dual-fuel system). Report each fuel type's consumption separately. The miles driven on CNG go on the CNG schedule with CNG rates; the miles driven on diesel go on the diesel schedule with diesel rates. You'll need to track which fuel the vehicle was consuming during each segment of driving, which typically requires onboard monitoring.

Are there states that don't participate in IFTA for alternative fuels?

All IFTA member jurisdictions participate in IFTA for all recognized fuel types. However, some states may not have published tax rates for less common fuels like methanol or E-85. In those cases, contact the jurisdiction directly to determine the applicable rate. Do not assume a rate of zero.

Bottom Line

Running a mixed-fuel fleet adds a layer of complexity to IFTA reporting, but the underlying math is the same: miles divided by MPG equals taxable gallons, multiplied by the tax rate. The key is keeping each fuel type completely separate — separate mileage tracking, separate fuel records, separate MPG calculations, and separate schedules on the return. Alternative fuels like CNG and LNG often carry lower IFTA tax rates, which can meaningfully reduce your quarterly bill. FleetCollect tracks miles by vehicle automatically, making it straightforward to group vehicles by fuel type and generate the per-fuel-type data you need for accurate multi-fuel IFTA reporting.