The newspaper, citing sources in the agency, said the announcement will be made Thursday at the North American International Auto Show in Detroit.
The new tests would give lower estimates of the number of miles a given make and model of car gets in city and highway driving. But they would also provide buyers with a more accurate picture of what they can expect in real life.
Consumer Reports, in a study last year, tested fuel efficiency estimates for 303 different types of cars. They found that the sticker estimates were optimistic for 90 percent of the cars and were off in some cases by as much as 50 percent.
The current tests were developed in the 1970s when the United States had a 55 mph national speed limit and traffic jams tended to be smaller.