Gasoline, Diesel, Hybrids And Plug-Ins: The Efficiency Leaders It's official: Cars really are getting more efficient. Not that there isn't a long way still to go, but virtually every month statistics emerge to suggest the average fuel efficiency of vehicles in the U.S. has gone up another few fractions of a percent. There are still winners and losers though, so we decided to think positive and look at the winners--just what are the most efficient gasoline, diesel, hybrid and plug-in vehicles available right now? Gasoline: 2013 Scion iQ 36 MPG city, 37 MPG highway, 37 MPG combined The 2013 Scion iQ sticks to a simple formula to achieve the gas mileage it does: A small, light body, a small-capacity gasoline engine, and that's about it. Several regular gasoline vehicles beat the iQ's 37 MPG highway figure--40 MPG is now not uncommon--but with a continuously-variable transmission and 1.3-liter engine it fights back with strong city mileage. The compact size makes it easy to drive in the city too, and even easier to park by the curb. Don't expect to take too many passengers though--it may be a four-seater by trade but you'll realistically fit no more than three, and you're better folding the rear seatback down and improving its luggage space. Diesel: 2013 Volkswagen Passat TDI 31 MPG city, 43 MPG highway, 35 MPG combined It's a Volkswagen-Audi washout at the top of the diesel charts, though that might change when the Chevrolet Cruze Clean Diesel and Mazda Mazda6 Sky-D both go on sale. Until then, the Passat TDI is the most efficient diesel model you can buy, and it's a particularly excellent highway performer. It uses the same 2.0-litre TDI engine as every other VW and Audi of this size or smaller, and offers a surprising turn of pace and excellent refinement for a diesel. Not a fan of the Passat's size or shape? Worry not--you can find the same engine, with barely lower fuel efficiency, in everything from the classy Audi A3, through the practical Jetta wagon, to the funky Beetle and Beetle Convertible models. Hybrid: 2013 Toyota Prius C 53 MPG city, 46 MPG highway, 50 MPG combined Both the Prius C and its larger, more iconic Prius stablemate achieve 50 MPG combined, and each offers slightly different strengths. The Prius C is cheaper, naturally, but it's also a little more agile and even better suited to city driving, with the higher city EPA rating. The regular Prius is the more spacious, and its superior aerodynamics and larger engine help it manage better highway figures. Plug-in hybrid: 2013 Toyota Prius Plug-In 51 MPG city, 49 MPG highway, 50 MPG combined, 95 MPGe blended The plug-in hybrid market is still relatively small right now, awarding the Prius top spot almost by default. It's selling in modest numbers and doesn't really break any new ground, but based on the already-efficient Prius it's always going to be inexpensive to run, particularly when that 11-mile electric and gas blended mode is considered--over which the Prius achieves 95 MPGe. Driving thrills aren't on the agenda, but the Prius should be trouble-free to own and relaxing to drive. Electric: 2013 Fiat 500e 122 MPGe city, 108 MPGe highway, 116 MPGe combined There are actually four answers to the question, "what's the most efficient electric car on sale?" Technically, the 2013 Scion iQ EV is--at 121 MPGe combined, or just 28 kWh per 100 miles. Only you can't get one for love nor money, which is poor even by compliance car standards. The Honda Fit EV is next up at 118 MPGe combined, but while you can at least put one on your driveway, it's lease-only. The 500e is the most efficient electric car you can actually buy and own, which is why we've awarded it the top spot. But if you wanted to go further, the 500e is still a compliance car and therefore only available to a very limited number of people--meaning the 115 MPGe, 29 kWh/100mi 2013 Nissan Leaf would actually come top. But for those who have access to one, it's the 500e that wins here. More fun than the Leaf, too.