The u. s. department of energy's fuel economy guide provides fuel efficiency data for cars and trucks (u. s. department of energy website, february 22, 2008). a portion of the data for 311 compact, midsize, and large cars follows. the column labeled class identifies the size of the car: compact, midsize, or large. the column labeled displacement shows the engine's displacement in liters. the column labeled fuel type shows whether the car uses premium (p) or regular (r) fuel, and the column labeled hwympg shows the fuel efficiency rating for highway driving in terms of miles per gallon. the complete data set is contained in the datafile named fueldata. click on the datafile logo to reference the data.