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Fuel economy for light vehicles sold in the U.S. could reach an average 43 mpg (5.5 L/100 km) by 2035, and alternatively powered vehicles may account for 20% of the cars and trucks sold, a new government report reveals.

However, such a jump from 27.6 mpg (8.5 L/100 km) today would require substantially higher petroleum prices, the U.S. Energy Information Admin. says in its annual energy outlook.

The government bases it prediction on oil costing $210 a barrel, up from an average of $61.66 in 2009 and $78.69 through the first six months of this year, as well as sales of 19 million vehicles with a mix tilting 69% towards passenger cars from 53% in 2009.

Under such a scenario, the average fuel economy for light vehicles would rise to 43 mpg, according to EIA.

But pricey crude alone won’t drive fuel economy higher, says Paul Holtberg, a spokesman for the EAI’s annual energy outlook. “Oil prices matter,” he tells Ward’s, “but technology and infrastructure matter, as well.”

That means items such as downsized engines with turbocharging and advanced aerodynamics, and greater availability of renewable fuels and electrified-vehicle charging stations.

For example, the government expects turbocharging, supercharging and cylinder deactivation to increase from 5% of light-vehicle sales in 2008 to 57% in 2035.