DETROIT (AP) — New cars and trucks sold in the U.S. last year got an average of 23.6 miles per gallon in combined city and highway driving, a record that came mainly through improvements to engines and transmissions, according to the Environmental Protection Agency.

Mazda led all automakers with an average of 27.1 mpg, followed closely by Honda with 26.6 and Volkswagen at 25.8. Chrysler-Fiat, which relies more on trucks and larger cars for its sales, had the worst mileage at 20.1, followed by Daimler, maker of Mercedes-Benz luxury vehicles, at 21.1. General Motors, which also sells a lot of trucks and SUVs, was third from the bottom at 21.7 mpg, according to the report.

The increase for 2012, the latest year for which full calculations are available, was 1.2 mpg above 2011's number, the second-largest annual increase in 30 years, the agency said in an annual report released Thursday. The EPA is estimating that the average mileage of 2013 cars will rise another 0.4 mpg to 24. Final figures for 2013 won't be available until next year.

Last year was the first year that automakers fell under more stringent government fuel economy regulations that require them to sell cars and trucks that get a combined 54.5 miles per gallon by 2025. Carbon dioxide emissions also are at a record low, 376 grams per mile.

Christopher Grundler, director of the EPA's office of Transportation and Air Quality, said many automakers already are meeting gas mileage standards for 2016 because of innovations. Automakers are offering more efficient engines, multiple-speed transmissions that keep engines at peak efficiency, and turbocharging that gives smaller engines more power when needed. They've also reduced weight by using lighter materials, powered more pumps off a battery rather than the engine to eliminate drag, and they've improved aerodynamics of new cars so they slice through the wind with less resistance.

Gasoline prices also were relatively high in 2012, and that helped steer people toward sales of more efficient vehicles, Grundler said. "Manufacturers and suppliers continue to develop great new technology," he said. "More consumers value fuel economy than in the past. So there was very strong demand."

Gas mileage is up 12 percent since 2008 and 22 percent since 2004, according to the report.

The government gas mileage requirements get tougher to meet as the years progress toward 2025, but Grundler said he's confident the auto industry has shown it has the kind of innovation needed to meet the challenge.

The cost of cars will rise gradually as automakers spend on new technology to get better mileage, but that will be more than offset by savings in gasoline spending, Grundler said.