What grade of gas is used for Nascar race cars?

NASCAR to Use Unleaded Fuel in 2008.

NASCAR announced that NASCAR teams would switch to unleaded fuel by the start of the 2008 season. This is a significant development for NASCAR teams as they have long been the target of environmental groups. This change is possible because researchers at Sunoco have developed Sunoco 260 GTX a new fuel formula that does not damage racing engines.

Beginning in 2011, Nascar started to use Sunoco Green E15 racing fuel. This is a renewable fuel blended with 15 percent American-made ethanol from American-grown corn.