S8 vs A8 quattro
Audi S8 against Audi A8 quattro, two test sheets laid side by side.
The gap, in fuel
$485a year between them
The Audi A8 quattro is more efficient — 22 MPG against 18 for the Audi S8. Over 15,000 miles a year at $3.20 a gallon that is a saving of about $485 a year, or $2424 over five years.
SOURCE·US EPA fuel-economy test data·FUEL ASSUMED AT $3.20/GAL FROM JUL 2026·REVIEWED JUL 2026
How this is worked out
- Start from the EPA combined figure for the model year — a laboratory test cycle run to a fixed procedure, not a road result. Where a year sold several engines or drivetrains, the trims are averaged and the trim count is printed beside the row so you can see how much averaging is behind it.
- Fix a pump price. This site keeps one reference price, $3.20 a US gallon, fixed JUL 2026 and printed next to every dollar figure it produces. It is an assumption with a date on it, not a quote — put your own price in.
- Fix an annual distance. Every annual figure on this site uses 15,000 miles a year, roughly the US average. A cost per year with no stated distance is not a number, it is a mood.
- Divide distance by economy for gallons, multiply by price for the year's fuel, divide price by economy for one mile. The per-kilometre line is that last figure divided by 1.609344 — the same money, in the unit most of the world drives in.
- Stop there. No depreciation, no tyres, no insurance, no servicing. This is the fuel line of the ledger and it is labelled as one; depreciation usually dwarfs everything on it.
gallons/yr = miles/yr ÷ MPG fuel $/yr = gallons/yr × $/gal cost $/mi = $/gal ÷ MPG cost $/km = cost $/mi ÷ 1.609344
The full method, the licence note, and what a test figure cannot tell you →
Both sheets, line for line
| Audi S8 | Audi A8 quattro | |
|---|---|---|
| Combined economy | 18 | 22 |
| Best year on record | 20 | 22 |
| Worst year on record | 15 | 18 |
| Average across all years | 17.2 | 20 |
| Fuel per year | 2667 | 2182 |
| Gallons per year | 833 | 682 |
| CO₂ g/mi | 502 | 414 |
| Model years tracked | 18 | 8 |
| Class | Midsize Cars | Midsize Cars |
| Years | 2003–2027 | 1999–2027 |
Highlighted cells are the better of the two on that measure. Fuel costs at $3.20/gal over 15,000 miles.
SOURCE·US EPA fuel-economy test data·FUEL ASSUMED AT $3.20/GAL FROM JUL 2026·REVIEWED JUL 2026
Questions asked across the counter
Which is more fuel efficient, the Audi S8 or the Audi A8 quattro?
The Audi A8 quattro is more efficient — 22 MPG against 18 for the Audi S8. Over 15,000 miles a year at $3.20 a gallon that is a saving of about $485 a year, or $2424 over five years.
Which is cheaper to run, the Audi S8 or the Audi A8 quattro?
On fuel alone, the Audi A8 quattro: $2182 a year against $2667 for the Audi S8, both at $3.20 a gallon over 15,000 miles — an assumption fixed JUL 2026. Fuel is the only line being compared: depreciation, insurance, tyres and servicing are not in it, and they routinely matter more than this gap.
Is the difference big enough to change the decision?
Across five years of that same driving the gap comes to about $2424. That is real money, and it is also roughly what one year of depreciation does to a new car — so treat it as one line in the ledger rather than the whole argument.
Open either logbook in full
Both entries carry the full year-by-year history and the pump-price ledger. Estimates based on official test figures and average fuel prices. Real-world consumption varies with driving style, load, terrain and maintenance.
