I have owned several 90's lesabre's and park avenue models, they all routinely got mileages in the 30 mpg range. many people have told me the same was common to buick's they had owned. this site rates them at 19 mpg must have a lead foot
According to the US government's website on fuel economy (http://www.fueleconomy.gov/), the supercharged version of this car gets 15 city and 24 highway (18 combined). This is only slightly worse than my 92 Buick Regal which has the same engine (supercharged) but is a smaller car. I consider it good gas millage; the only alternative in '92 would have been a V8 (which I actually wish had been the route GM had taken; I unfortunately have to look to Ford for a decent car with a V8 from this era).