New cars and trucks sold in the United States 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, the Environmental Protection Agency said.

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, 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 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.