Passenger cars averaged a new high of 31.2 mpg in the first half of 2008 -- the same as in 2007.

Light trucks averaged 23.4 mpg -- up from 23 mpg in the 2007 model year. Both figures handily beat the government's 2007 mileage mandates of 27.5 mpg for passenger cars and 22.2 mpg for light trucks.

Congress last December ordered automakers to hike fuel efficiency to a fleet wide average of 35 mpg by 2020 -- a 31 percent increase over the current industry average.

In April, NHTSA proposed hiking fuel efficiency requirements to 28.6 mpg for light trucks and 35.7 mpg for passenger cars by the 2015 model year -- ahead of the minimum requirements set by Congress. Automakers want NHTSA to soften its proposed increase before it makes it final by year's end. NHTSA said it estimated it would cost automakers $47 billion through 2015 to meet its proposed increases.

NHTSA calculates the average of passenger cars built in the United States and Canada, along with imports. Here's how the top automakers fared:

• General Motors Corp.: 29.4 mpg for domestic cars, 31.5 mpg for imported vehicles and 22.5 mpg for light trucks.

• Ford Motor Co.: 29.5 mpg for domestically produced cars, 30.1 mpg for imported cars and 23.2 mpg for light trucks.

* Chrysler LLC: 29.3 mpg for domestic vehicles, 27.2 mpg for imported vehicles and 23.6 mpg for light trucks.

• Toyota Motor Corp.: 34.7 mpg for domestically produced cars, 37.9 mpg for imported cars -- including Prius hybrids -- and 24.0 mpg for light trucks.

• Honda Motor Co.: 35.2 mpg for domestically produced cars, 33.2 mpg for imports, and 25.4 mpg for light trucks.

• Nissan Motor Co.: 28.8 for imported cars, 33.5 mpg for domestically produced cars and 23.2 mpg for light trucks.

Beth Lowery, General Motors Corp.'s vice president for energy and environment said the final model year average for the industry would be even higher in the wake of the dramatic run-up in oil prices that has radically shifted consumer demand to more efficient, smaller vehicles.