The U.S. Department of Energy today released estimates of “eGallon” prices designed to help car buyers better understand the operating savings from driving electric vehicles.

The new Energy.gov/eGallon Web site includes prices for an eGallon nationally and by state compared to the price for a gallon of gasoline.

In Oregon, the electric car savings is $2.78 per gallon, the site estimates. The savings is a bit smaller nationally – $2.51 – because of Oregon’s lower electricity costs and higher gasoline prices.

Some calculation details:

In Oregon, a gallon of gas runs $3.74, the site says. That gallon would move the typical car 28.2 miles, based on the combined mpg for the U.S. small and mid-size fleet.

To drive 28.2 miles, the 5 top selling all-electric and plug-in hybrid vehicles nationally – the Chevy Volt is No. 1 – would need 96 cents of electricity at Oregon’s electricity prices. That’s a $2.78 savings per gallon.

Prices for electric cars run higher. At the Portland International Auto Show in January, a Chevy Volt with a $42,780 sticker price sat side by side with a $26,690 Chevy Cruze, the Volt’s all-gasoline counterpart.

Even after a federal tax credit of up to $7,500, it would take nearly a decade to pay back the extra purchase cost through fuel savings alone, based on annual fuel costs listed on the cars’ stickers.

But the eGallon should give buyers a better sense of operating savings, the energy department says, with a metric that’s comparable to the often dismaying gas price signs drivers see every day.