Quick answer
Diesel typically pencils out cheaper than gas per mile for vehicles driving 15,000+ highway miles a year, because diesel's 20–30% MPG advantage usually outweighs the 5–20% price premium per gallon. For short, urban trips it's often a wash or worse.
The honest comparison
Per-gallon price is a red herring. Compare on cost per mile — see how to calculate fuel cost per mile for the formula.
| Gas pickup | Diesel pickup | |
|---|---|---|
| Price / gal | $3.40 | $3.85 |
| MPG (highway) | 22 | 28 |
| Cost / mile | $0.155 | $0.138 |
| 15,000 mi / yr | $2,325 | $2,070 |
Same miles, ~$255/year cheaper on diesel — before maintenance.
Where diesel's edge gets eaten
- Diesel exhaust fluid (DEF): $15–$25 per fill, every few thousand miles.
- Oil changes: larger sumps, longer intervals, but each service costs more.
- Fuel filters and injectors: diesel components are pricier when they fail.
- Cold-weather operation: winter fuel additives and harder starts.
A reasonable rule of thumb: add $300–$600/year to diesel's operating cost for a light-duty pickup. That can close most of the fuel-savings gap on lower-mileage drivers.
Where diesel wins anyway
- Towing and payload: diesels do hard work cheaper per mile.
- Long-haul driving: the MPG gap is biggest at steady highway speeds.
- Resale value: diesel light trucks routinely hold value better than gas equivalents.
- Fuel-card discounts: diesel-focused cards (Comdata, EFS, Fuelman, WEX OTR) often offer meaningful per-gallon savings — see fuel cards for the landscape.
When gas is the right answer
City commuters under 12,000 miles a year, occasional drivers, and anyone who doesn't tow rarely recoup diesel's purchase premium and maintenance overhead. Gas is also simpler — fewer emissions systems to maintain.
How to decide
- Estimate your annual miles and split (highway vs. city).
- Use realistic MPG numbers — not the window sticker.
- Run cost per mile for both options in the fuel cost calculator.
- Add ~$400/yr to diesel for maintenance and DEF if you're driving a light-duty truck.
- Subtract any fuel-card discount you'd actually use.
If diesel still wins by enough to justify the purchase premium over your ownership horizon, buy diesel. Otherwise, gas.
About these numbers
Prices, MPG, and maintenance figures in this guide are estimates from public sources and FuelHere reader benchmarks. Real numbers vary by region, model year, and driving style. Verify against your own data before buying a vehicle.
