Hybrid and diesel SUVs combine the interior space and ride quality of an SUV with fuel-saving capabilities of hybrid cars. Some environmentalists have criticized the hybrid SUV as a misapplication of gas-electric technology. It’s true that hybrid SUVs do not reach the level of fuel efficiency of smaller hybrids in terms of miles-per-gallon. Yet, miles-per-gallon is a non-linear and counter-intuitive form of measurement. An apparently small jump in fuel efficiency—for example, from 14 to 16 mpg—saves as much oil as increasing fuel economy from 35 to 50 mpg, according to the Union of Concerned Scientists.