Fiat Chrysler Automobiles NV, which lags the auto industry in fuel efficiency, purchased U.S. greenhouse gas emissions credits from rival automakers Toyota Motor Corp, Tesla Motors Inc and Honda Motor Co, a government report released on Wednesday show.

The Environmental Protection Agency said Wednesday that the Italian American automaker has purchased about 8.2 million megagrams of emissions credits. 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. The report shows trading in credits jumped by nearly 400 percent in the 2014 model year - the most recent for which data is available.

Even without acquiring credits, Fiat Chrysler still would have been in compliance in the 2014 model year, the report said.

"We have made significant strides – often exceeding industry averages – in improving the performance of those types of vehicles most preferred by our customers," the company said.

Fiat Chrysler said it earned credits for making improvements to air conditioning systems and other technological improvements.

Fiat Chrysler, which previously purchased nearly 1.7 million megagrams of emissions credits from Tesla, Nissan Motor Co and Honda, acquired another 6.5 million credits through the end of the 2014 model year, the report shows.

Fiat Chrysler ranked last among major automakers with a fleetwide fuel efficiency of 20.8 miles per gallon for the 2014 model year and is projected to nearly tie General Motors Co in the 2015 year at 21.8 mpg for last place, EPA said.

The new purchases include 5.5 million in credits from Toyota and Honda and about 1 million from Tesla.

Fiat Chrysler had a credit balance of 13.8 million credits at the end of the 2014 model year.

This is the first time Toyota has chosen to sell credits.

Daimler AG's Mercedes-Benz unit has acquired about 1.4 million credits, including 500,000 additional credits from Nissan, according to the report. Without the credits, it would be in a deficit since it had about 200,000 credits remaining at the end of 2014.

Ferrari NV, which was spun off by Fiat Chrysler earlier this year, acquired another 175,000 credits and has purchased 265,000 credits.

Tesla sold all of its 2013 and 2014 greenhouse gas emissions credits to Fiat Chrysler. Tesla earned $216.3 million in all regulatory credit sales in 2014 and $194.4 million in 2013 but does not breakout transactions.

(Reporting by David Shepardson; Editing by Bill Trott)