(Corrects percentage in headline and lead)

LA JOLLA, Calif., May 13 (Reuters) - Ethanol could replace up to 20 percent of gasoline supplies in the United States and Europe, Tony Hayward, CEO of oil major BP BP.L, said on Wednesday.

Ethanol currently accounts for about 7 percent of U.S. gasoline demand, according to industry groups. (Reporting by Robert Campbell)