Who needs hybrids to hit higher fuel economy targets? For the fourth year running, the US Environmental Protection Agency (EPA) has declared Mazda the most fuel efficient auto manufacturer in America. Its current eight-model vehicle range -- from the drop-top two-seat MX-5 Miata to its flagship seven-seat CX-9 crossover -- boast a fleet-wide average fuel economy of 29.6 MPG and it's all down to clever engineering of traditional internal combustion engines and the stripping of extra weight from body panels, rather than adding battery packs or moving into full plug-in electric vehicle market.

"Mazda's team of engineers and designers have worked diligently to create vehicles that are high-quality, stylish, fun-to-drive and fuel-efficient," said Masahiro Moro, president and CEO, Mazda North American Operations.

According to the EPA, of the country's 12 biggest car companies (sales of 100,000 per year or more are required to make it on the list -- hence no Tesla), the overall trend across the industry is decreased CO2 emissions and higher fuel economy.

The average new car in the US now achieves a record 24.8mpg. All of the biggest car companies have met or exceeded the 2015 model year CO2 emissions standards by an average of 7g/CO2 per mile. What's more, eight car companies have managed to better that record 24.8mpg fuel economy average.

Honda's efficiency over the past 12 months has jumped to 28.9mpg, putting the marque in second place despite having a much larger fleet of vehicles than Mazda, including pickup trucks. However, it also has hybrids in its range helping to keep average fuel consumption down.

But the company that made hybrids fashionable, Toyota, finds itself down in eighth place with a 25.2mpg average behind BMW (26.3mpg) in seventh but well ahead of Mercedes (23.5mpg) in ninth place.

The least economical car company in this year's report is the Fiat Chrysler Group (21.8mpg) but, as the EPA notes, it is also the most improved company, cutting CO2 emissions by a huge 21% over the past 12 months and boosting fuel economy by a full 1%.

Since the National Greenhouse Gas and Fuel Economy standards for passenger vehicles were introduced in 2012, average fuel economy has improved by over 2mpg and CO2 emissions have fallen by as much as 10%. The EPA notes that it has seen improvements in every vehicle class from sportscars to SUV and pickup truck as well as sedans and mini vans.

"Car buyers can go to the showroom knowing that no matter what kind of vehicle they buy, it will be better for the climate -- and their wallets -- than ever before," said Christopher Grundler, director of EPA's Office of Transportation and Air Quality. "The industry is providing vehicles that customers want, while reaching new levels of environmental performance."