Gas mileage in the 2012 Buick Regal isn't quite as good as some of the class leaders, but it's still a big improvement over the last generation of mid-size family sedans.
The base Regal, with four-cylinder engine and automatic transmission, is rated by the EPA at 19/31 mpg. It's a bit shy of the standard set by cars like the Ford Fusion, at 33 mpg highway, or the Hyundai Sonata and similar Kia Optima, at 35 mpg highway.
Opt into a turbocharged Regal, and mileage actually goes up, since a manual transmission is offered. That six-speed manual Regal earns a 20/32 mpg rating, with the automatic checking in at 18/29 mpg. The Regal GS, with its additional power, is a bit lower, at 19/27 mpg for the manual-shift model (automatic versions are coming, but haven't yet been rated).
The big news for fuel economy is with the eAssist model coming later this model year. With lithium-ion batteries and electric motors, it has some of the components of a hybrid, and it's classified by the EPA as a hybrid -- but GM prefers to dial down the "hybrid" for its marketing, since eAssist is a bit more limited than full hybrid vehicles. The Regal's variation on hybrid technology uses batteries and motors to boost acceleration under heavy acceleration, and to run accessories such as air conditioning, but the Regal can't run on electric power alone.
The eAssist is rated at 25/36 mpg. That's not much higher than the base Sonata and Optima, and can't rival their 40-mpg highway ratings--or that of the 43-mpg diesel VW Passat. But eAssist does put the Regal on even keel with vehicles like the Lincoln MKZ Hybrid and the Lexus HS 250, while still pricing in at less than $30,000.