Buick added two variants to the Buick Regal for the 2012 model year, including the eAssist and GS trims. The eAssist powertrain, which is GM’s second-generation mild-hybrid system, offers similar power but up to 36 mpg highway compared with the Regal’s current standard four-cylinder. The top-of-the-line GS trim offers better power than other Regals, but it’s still not quite a performance machine, Cars.com Industry Analyst Kelsey Mays says.