All-electric cars are the most efficient ones among all types of drivetrains, followed by plug-in hybrids.

This fact is confirmed by the official Fueleconomy.gov data, which compares MPG for conventional cars with MPGe equivalent (33.7 kWh = 1 gal. of gasoline) for EVs, under three categories - combined & city/highway ratings.

Among the 10 best 2015 models, there are only all-electric cars, and the worst combined results were above 100 MPGe.

Top Fuel Sippers (EPA Ratings, 2015 Model Year)

Top Fuel Sippers (EPA Ratings, 2015 Model Year)

When we switch to the another comparison, for all-years and exclude all-electric cars, we can see that BMW i3 is a double winner.

According to the EPA, Chevrolet Volt has just slightly better fuel economy than the Toyota Prius Plug-In Hybrid.

The best conventional hybrid cars in 2015 stand at 50 MPG, while Volts and other PHEVs often get a lot fuel economy in real world driving if all-electric mode is used often.

Top Fuel Sippers (EPA Ratings, All Years) (all-electric vehicles are excluded)

Top Fuel Sippers (EPA Ratings, All Years) (all-electric vehicles are excluded)