Originally Posted by flars
Bad odometer??
Fuel leak?
There's no smell of fuel nor are there any stains on the ground where it's parked, so most likely not the culprit.

However, the odometer it a thought. Since we know the BMW speedos are always way off, mine shows almost 10mph higher than actual speed when I'm on the highway...so 75mph is actually closer to 65mph, which means the odometer would be rounding up by at least 10-15%. That means that if the odometer shows 100 miles for four gallons used then in reality it was 90 miles and then my 25mpg becomes more like 21-23mpg.

Bad to worse!