Two Sedans with more similarities, such as the body structure, starting price, ground shadow size, height, and maximum occupancy, than differences, like the powertrain, horsepower, and fuel economy. First of all, the 2016 Buick Regal has bigger and thirstier engine; the 2015 Volkswagen Passat Diesel gets 10.3 more mpg. Among similarities are the body structure, starting price, ground shadow size, height, and maximum occupancy.