Gas mileage comparison is difficult because some vehicles give their best on highways while some are too good on city roads. A car that can be most fuel-efficient in one country need not be same good performer in the entire world. Performance of car also depends on fuel used and maintenance. Mileages given by vehicles differ at same quantity of gas.
There are examples of vehicles with same engines deliver same mileages, so we cant have gas mileage comparison between them. The two wheel drive versions of Toyota Highlander Hybrid and Lexus RX 400h have 3.3-liter six-cylinder engine, which deliver 28 city and 25 highway miles per gallon. Both versions have 3.3-liter six-cylinder engine and even the mileage delivered by both versions is same. Ford Escape Hybrid 4WD and Mercury Mariner Hybrid 4WD use 2.3-liter four-cylinder engine and delivers 28 city and 27 highway miles per gallon. Even in this case, both sports utility vehicles use 2.3-liter four-cylinder engine and deliver the same mileage of 28 city and 27 highway miles per gallon.
Some examples are of vehicles with same engines and different mileages. In this case, gas mileage comparison can be done. Logically engines of same power should deliver same mileages. But two SUV's like Ford Escape Hybrid FWD and Ford Escape Hybrid 4WD use same power engine i.e. 2.3 liter four cylinders engine.
The mileage delivered by Ford Escape Hybrid FWD is 31 city and 29 highway miles per gallon while Ford Escape Hybrid 4WD is 28 city and 27 highway miles per gallon. Saturn Vue Hybrid and Jeep Compass 4WD use 2.4 liter four cylinders engine but deliver mileages of 23 city and 29 highway miles per gallon and 22 city and 27 highway miles per gallon respectively. Chevrolet HHR FWD and Honda Element 2WD use 2.4 liter four cylinders engine but deliver mileages of 21 city and 28 highway miles per gallon and 20 city and 25 highway miles per gallon respectively. Mercedes-Benz GL320 CDI 4matic and Mercury Mariner 4WD use 3 liter six cylinders engine but deliver mileages of 18 city and 23 highway miles per gallon and 17 city and 21 highway miles per gallon respectively.
Gas mileage comparison is possible even in the case of different powered engines but same mileages delivered. Logically engine with more power should deliver more mileage than the engine with less power. But there are the vehicles having same engine but still they deliver different mileages.
Infiniti FX45 AWD and Chevrolet Suburban 1500 4WD use 4.5 liter eight cylinders engine and 6 liter eight cylinders engine respectively but the mileage delivered is same 13 city and 17 highway miles per gallon. Dodge Durango 2WD and Nissan Armada 2WD use 4.7 liter eight cylinders and 5.6 liter eight cylinders respectively but the mileage delivered is same as 9 city and 13 highway miles per gallon. Toyota RAV4 4WD and Mercedes-Benz R320 CDI 4matic use 3.5 liter six cylinders and 3 liter six cylinders respectively but the mileage delivered is 19 city and 26 highway miles per gallon.
