The U.S. Environmental Protection Agency said the fuel economy for new vehicles hit a new high in the 2020 model year at 25.4 miles per gallon but most automakers relied on credits to meet federal emissions requirements.
The report said since 2004, carbon dioxide emissions have decreased by 24% as fuel economy has improved by 32%.
The report said only Tesla Inc, Subaru and Honda met requirements without using credits. Automakers can either purchase credits or use credits earned from earlier model years.
Detroit's Big Three automakers -- General Motors , Ford Motor Co and Chrysler parent Stellantis -- had the lowest average fleetwide fuel economy in 2020 in part because they sell more large trucks and sport utility vehicles than other automakers.
GM and Ford both averaged 23 miles per gallon, while Stellantis averaged 21.8 mpg. Tesla, which only makes electric vehicles, led the industry, while Honda averaged 29.1 mpg, which was first among automakers building gas-powered vehicles.