Managing a mixed fleet that runs both diesel and gasoline vehicles adds a layer of complexity that single-fuel operations never face. Price differentials between the two fuel types can swing by 50 cents or more per gallon depending on the region and time of year. Having the right fleet cards in place allows managers to track spending by fuel type, negotiate separate discount tiers, and identify which vehicles and routes are consuming the most budget.
The data-driven approach to fuel management has become standard practice in 2026. Fleet operators who use a business gas card program with analytics capabilities can break down costs per mile for each vehicle, compare fuel economy across their diesel and gasoline segments, and make informed decisions about future vehicle purchases based on actual operating costs rather than manufacturer estimates.
How Diesel and Gasoline Costs Compare
Diesel historically costs more per gallon than regular gasoline, but diesel engines deliver 25-35% better fuel economy per gallon. This means the cost-per-mile calculation often favors diesel for heavy-duty applications even when pump prices are higher. However, diesel price volatility tends to exceed gasoline volatility because diesel is also used for heating oil and industrial applications, creating seasonal demand spikes that do not affect gasoline.
| Factor | Diesel Fleet | Gasoline Fleet |
|---|---|---|
| Average cost per gallon (2026) | $3.85 - $4.25 | $3.15 - $3.55 |
| Fuel economy advantage | 25-35% better per gallon | Baseline |
| Price volatility | Higher (seasonal swings) | More stable |
| DEF fluid requirement | Additional cost ($3-6/gallon) | Not required |
| Engine maintenance costs | Higher (injectors, turbos) | Lower maintenance baseline |
Why Mixed Fleets Need Specialized Tracking
When a fleet operates both fuel types, aggregate fuel spending numbers hide important details. A diesel truck averaging 6 miles per gallon and a gasoline van averaging 18 miles per gallon have completely different cost profiles that demand different management strategies. Fuel card programs that separate reporting by fuel type allow managers to benchmark each vehicle against others in its class, identify units that are underperforming their expected fuel economy, and calculate the true total cost of ownership for each vehicle type.
Diesel Fleet Advantages
- Superior fuel economy for heavy loads
- Longer engine lifespan (500,000+ miles)
- Higher torque for towing and hauling
- Better resale value for commercial vehicles
- More efficient at sustained highway speeds
Gasoline Fleet Advantages
- Lower upfront vehicle purchase cost
- Cheaper per-gallon fuel pricing
- No DEF fluid expense or maintenance
- Wider mechanic availability for repairs
- Quieter operation for urban routes
Discount Structures Differ by Fuel Type
Major fuel card providers often structure their diesel and gasoline discounts differently. Diesel discounts tend to be larger in absolute terms because the per-gallon price is higher and commercial diesel volumes are larger. Some programs offer tiered discounts where the rate improves as monthly volume increases, creating stronger incentives for fleets that can concentrate their purchasing. Gasoline discounts may be structured as a flat per-gallon rate regardless of volume, making them more predictable but potentially less valuable for high-volume operations.
The DEF Factor
Diesel Exhaust Fluid has become an unavoidable cost for diesel fleets running vehicles manufactured after 2010. At $3 to $6 per gallon with consumption rates of roughly one gallon per 100 gallons of diesel, DEF adds a meaningful cost that does not appear in fuel card data unless the program specifically tracks it. Comprehensive fuel card programs now include DEF purchases in their analytics, giving fleet managers a complete picture of diesel operating costs rather than just the fuel itself.
Making the Right Fleet Composition Decision
Fuel card data over 12 or more months provides the clearest picture of which fuel type performs better for specific routes and applications. Short urban delivery routes almost always favor gasoline vehicles due to lower purchase costs and the fuel economy penalty diesel engines suffer in stop-and-go conditions. Long-haul routes with heavy payloads consistently favor diesel because the fuel economy advantage compounds over distance. Having detailed per-vehicle, per-route cost data from fuel card programs transforms this decision from guesswork into data-driven fleet planning.
Sources: EIA Petroleum Price Data 2026, Fleetio State of Fleet Management Survey, Fortune Business Insights Fuel Card Market Report, FleetRabbit Fleet Management Guide