DETROIT — The government says the nation’s cars and trucks are well on their way to meeting fuel economy and emissions standards set for 2025.

But if gas prices stay low and consumers keep buying less-efficient vehicles like SUVs, the government could lower those standards. Automakers argue that meeting the requirements is difficult.

A report on the standards was issued Monday by the U.S. Environmental Protection Agency, the U.S. Department of Transportation and the California Air Resources Board. The report kicks off a two-year review that will determine whether to keep the 2025 fuel economy and greenhouse gas emissions targets in place.

Under standards set in 2012, automakers’ fleets were expected to get an average of 54.5 miles per gallon by 2025. That’s not the real-world mileage vehicles will get; it includes credits for things like more efficient air conditioning systems. The real-world mileage is closer to 40 miles per gallon.

The government calculates an automakers’ average based on the vehicles it sells. A company could fail to meet standards on pickup trucks but exceed them with fuel-efficient cars and still meet the requirements. But if it fails to sell those cars, it could wind up being fined.

As gas prices have fallen, truck and SUV sales have risen. That means the 54.5 mpg standard may no longer be realistic, since automakers are selling more trucks and SUVs and fewer cars than the government anticipated in 2012.