The US government Thursday finalized new automobile fuel economy standards starting with 2012 models, a move officials said would save billions of barrels of oil and reduce greenhouse emissions.

The rules announced by the Department of Transportation and Environmental Protection Agency "will significantly increase the fuel economy of all new passenger cars and light trucks sold in the United States," the agencies said.

"The rules could potentially save the average buyer of a 2016 model year car 3,000 dollars over the life of the vehicle and, nationally, will conserve about 1.8 billion barrels of oil and reduce nearly a billion tons of greenhouse gas emissions over the lives of the vehicles covered."

Starting with 2012 model year vehicles, the rules require automakers to improve fleet-wide fuel economy and reduce fleet-wide greenhouse gas emissions by roughly five percent every year.

By 2016 the industrywide standard will be 34.1 miles (54.9 kilometers) per gallon (3.8 liters), taking into account improvements in efficiency of car air conditions.

The standards also require that by the 2016 model-year, manufacturers must achieve a combined average vehicle emission level of 250 grams of carbon dioxide per mile.

"These historic new standards set ambitious, but achievable, fuel economy requirements for the automotive industry that will also encourage new and emerging technologies," said Transportation Secretary Ray LaHood.

"We will be helping American motorists save money at the pump, while putting less pollution in the air."

In a simultaneous move, Canadian Environment Minister Jim Prentice also announced new vehicle emissions standards would be applied on passenger cars and light trucks imported or manufactured in Canada and the United States.

The regulations affect 2011 and later model year vehicles, and are expected to cut 92 megatons of CO2 emissions over the lifetime of 2011-2016 model year vehicles sold in Canada, a statement said.

"Yes, vehicles will cost a little more up front, but the money saved on fuels should make up for the extra cost," Prentice told a press conference at a local Ford dealership.

"In the end, by 2016, they will be 25 percent more fuel efficient than they are now."

The moves were hailed by the Environmental Protection Agency administrator Lisa Jackson.

"This is a significant step towards cleaner air and energy efficiency, and an important example of how our economic and environmental priorities go hand-in-hand," she said.

DOT and EPA received more than 130,000 public comments on the September 2009 proposed rules before issuing the final standards.

Officials said the program would reduce carbon dioxide emissions by about 960 million metric tons over the lifetime of the vehicles regulated, equivalent to taking 50 million cars and light trucks off the road in 2030.

Later in the year, Canada and the United States are expected to announce continental emissions standards for passenger trucks and heavy trucks, as well as for ships and trains.

Canada's Prentice also hinted at a continent-wide emissions credit system.