EPA says Mazda's 27.5 mpg average makes it most fuel-efficient automaker in US.

Zoom-Zoom, indeed. Toyota may be the world's biggest maker of hybrids and Nissan may be making big strides on the plug-in front with increased sales of its Nissan Leaf electric vehicle, but it's Japanese automaker Mazda that has once again topped the Environmental Protection Agency's (EPA) list of most fuel-efficient automakers selling vehicles in the US, increasing its Model Year 2012 average by half a mile per gallon compared to MY2011.

Mazda wins with a 27.5 mpg average.

According to the EPA's "Trends" report (PDF), Mazda not only had the highest fleetwide fuel economy last year, but it also had the lowest emissions rate among the 11 largest automakers in the US. Mazda boosted its 2013 model-year fuel economy to 27.5 miles per gallon, up from 27 mpg. The company's fleetwide emissions fell to 324 grams of CO2 per mile, down from 328.

Honda came in second on the fuel-economy front with an even 27 mpg, while Volkswagen and Subaru tied for third at 26.2 mpg. Chrysler/Fiat filled out the bottom of the list with 21.6 mpg, just beaten by General Motors with 22 mpg. Chrysler/Fiat did have the largest year-over-year fuel economy jump at 1.5 mpg, however.

Mazda has eschewed hybrid and plug-in powertrains in favor of its more efficient Skyactiv engines and platform development technologies, and it also doesn't offer many large vehicles – its CX-9 crossover sells in modest numbers and it doesn't offer any pickups. After years of slow sales, Mazda finally appears to be on to a winning formula, announcing plans in August to Skyactiv engine production because of stronger-than-expected sales. Mazda expects to sell 1.7 million vehicles worldwide by 2016, and Skyactiv engines are expected to account for 80 percent of those sales.

Source: EPA, Mazda via Hybrid Cars