Model-year 2012 vehicles achieved an all-time high fuel economy of 23.6 miles per gallon (mpg), according to a report released by the U.S. Environmental Protection Agency.

This represents a 1.2 mpg increase over the previous year, making it the second largest annual increase in the last 30 years. Fuel economy has increased by 2.6 mpg, or 12 percent, since 2008, and by 4.3 mpg, or 22 percent, since 2004.

The EPA's annual report, "Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 through 2013," attributes much of the recent improvement to the rapid adoption of more efficient technologies such as direct-injection engines, turbochargers, and advanced transmissions.

Mazda achieved the highest fleet-wide rating at 27.1 mpg, a 2.1 mpg improvement from 2011. Honda and Toyota placed second and third with a rating of 26.6 mpg and 25.6 mpg respectively. Ford was the highest U.S.-based automaker on the list at 22.8 mpg. GM reached 21.7 mpg and Chrysler came in with a 20.1 mpg.

Fuel economy is expected to continue improving under the Obama administration's National Clean Car Program standards. The program expects to double fuel economy standards by 2025 and cut vehicle greenhouse gas emissions by half.

Despite the more fuel-efficient engines, vehicle performance hasn't suffered, according to the report. The average car still reached o to 60 mph in 9.4 seconds, which was unchanged from 2011 data. While average power fell by 8 horsepower to 222 hp in 2012, average vehicle weight fell by 150 pounds.

In its report, the EPA noted that adjusted fuel economy values reflect real-world estimates and are not comparable to automaker standards compliance levels. Adjusted economy values are about 20% lower, on average, than non-adjusted fuel economy values.