The Cadillac STS does 18.9 mpg combined (16 city, 24.8 highway), which works out to about $2,032 a year in fuel at $3.20 a gallon and 12,000 miles. Engine choice matters more than you'd think: 3.6L 6-cyl does 19.7 mpg while 4.6L 8-cyl does 18 — a difference of $184 a year. Against other V6 cars it sits below the average of 19.9 mpg.
Every Cadillac STS engine, compared
Gas mileage on the Cadillac STS ranges from 19.7 down to 18 depending on which engine sits under the bonnet — a spread of $184 a year across 2 versions of the same car. Picking the right one often saves more fuel than picking a different car altogether. Yearly cost assumes 12,000 miles at $3.20 a gallon.
| Engine | Combined | City / Highway | Years | Fuel per year |
|---|---|---|---|---|
| 3.6L 6-cyl | 16.9 / 25.6 | 2005–2011 | $1,949 | |
| 4.6L 8-cyl | 15 / 23.8 | 2005–2010 | $2,133 |
What that actually costs
The Cadillac STS burns a gallon every 18.9 miles, so 12,000 miles takes about 635 gallons a year. At $3.20 that is what the table below adds up to.
| Measure | Value |
|---|---|
| Cost per mile | $0.169 |
| Fuel per year | $2,032 |
| Fuel over five years | $10,160 |
| Against other V6 cars | +$102 a year |
| EPA's own estimate | $3,623 a year |
City or highway — who is this car for
The Cadillac STS gives up 8.8 mpg the moment you leave the motorway — 24.8 out there against 16 in town, a 55% drop worth $852 a year. A wide gap punishes stop-and-start traffic; a narrow one means the car doesn't care where you drive it.
| Measure | Value | Reading |
|---|---|---|
| City | 16 mpg | $2,400 a year if you only drive in town |
| Highway | 24.8 mpg | $1,548 a year if you mostly commute |
| Gap | +8.8 mpg (55%) | Wide — this car dislikes traffic |
How the STS changed over the years
The STS peaked in 2011 at 21 mpg (18 city, 27 highway) and was at its thirstiest in 2005 at 18 — 3 mpg apart, or $304 a year in fuel between buying one year and the other. The 2011 car does 21. Jumps usually mark a new generation or a new engine; dips often mean a heavier body or added all-wheel drive.
| Model year | Combined | City / Highway | Engines offered | Fuel per year |
|---|---|---|---|---|
| 2011 | 18 / 27 | 1 | $1,829 | |
| 2010 | 16.5 / 25.5 | 2 | $1,969 | |
| 2009 | 16 / 25 | 2 | $2,021 | |
| 2008 | 16 / 25 | 2 | $2,021 | |
| 2007 | 15.5 / 24.5 | 2 | $2,076 | |
| 2006 | 15.5 / 24.5 | 2 | $2,076 | |
| 2005 | 15.5 / 23 | 2 | $2,133 |
MPG is a number. Dollars per year is the answer.
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How we count
This page rests on 13 EPA ratings of the Cadillac STS — 2 engines across 2005–2011. The mileage is EPA's laboratory figure, unchanged; the yearly bill is ours, at 12,000 miles and $3.20 a gallon, against EPA's own estimate of $3,623. Full method.
Frequently asked questions
What mpg does the Cadillac STS get?
18.9 mpg combined on average — 16 in the city and 24.8 on the highway, per EPA ratings across 2005–2011.
How much does a Cadillac STS cost in fuel per year?
About $2,032 at 12,000 miles and $3.20 a gallon — roughly $10,160 over five years, or 0.169 dollars a mile.
Which STS engine is the most economical?
The 3.6L 6-cyl at 19.7 mpg, against 18 for the 4.6L 8-cyl — a difference of about $184 a year.
Is the STS good on fuel compared with similar cars?
Against other V6 cars it sits below the average of 19.9 mpg, computed across 4940 ratings.
Are these real-world STS figures?
No — they are EPA laboratory ratings, the same ones printed on the window sticker, and EPA's own annual fuel estimate for the Cadillac STS is $3,623 against the $2,032 we compute at 12,000 miles. Expect a little worse in practice: the spread between the 21 and 18 mpg versions of this car is smaller than the spread between two drivers of the same one.
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