According to the EPA, V6-equipped 2006 Buick Lucernes should return 19 mpg in the city and 28 mpg on the highway, running just fine on 87-octane gasoline. Eight-cylinder models require premium fuel and those extra ponies make a dent in fuel economy, offering 17 mpg in the city and 25 mpg on the highway. Our test drive of a V8 model returned 17.2 mpg overall.