(Adds details from report, background)
WASHINGTON, Jan 11 (Reuters) - The fuel economy of new U.S. cars and trucks hit a record 24.7 miles per gallon in the 2016 model year, a government report said, even as regulators consider whether to revise fuel efficiency requirements.
Fuel economy rose by just 0.1 mile per gallon in 2016 and is projected in the 2017 model year to hit another record of 25.2 mpg, the U.S. Environmental Protection Agency said in a report.
With low oil prices and Americans buying more trucks and SUVs, automakers have been concerned that rising fuel efficiency requirements through 2025 may be too stringent.
Environmentalists say automakers must do more to make vehicles more efficient.
The report said that after running surpluses in meeting greenhouse gas emission limits, automakers ran a 9 gram per mile deficit. The EPA said all major automakers still comply with the standards, with some using credits banked from prior years to meet the requirements.
Two automakers -- Volvo and Jaguar Land Rover -- have emission deficits, but they have three years to come into compliance.
Fiat Chrysler Automobiles NV had the biggest deficit, falling 28 grams per mile of the requirements. But the company had credits banked to meet the requirements.
The company purchased nearly 2.5 million megagrams of emissions credits in 2016 from Tesla Inc, the EPA said. A megagram is equal to 1,000 kilograms and is calculated on emissions saved over legal requirements.
The government does not disclose how much automakers pay for credits. Since 2010, Fiat Chrysler has purchased 22 million megagrams of credits from other automakers, including nearly 6 million from Tesla.
Mazda Motor Corp led the industry in average fuel economy at 29.6 mpg in 2016, but Honda Motor Co is projected to surpass Mazda as the leader in 2017.
Detroit's Big Three automakers -- including General Motors Co and Ford Motor Co -- had the least fuel-efficient fleets overall. They sell a larger share of pickup trucks and SUVs than their foreign rivals.
The EPA report measures real world fuel economy, which is less than the values listed on new vehicle window stickers.
(Reporting by David Shepardson; Editing by Bernadette Baum)