RIO DE JANEIRO (Reuters) - Chevron , the second-largest U.S. oil company, faces problems regaining its Brazilian oil-drilling rights because it hasn't explained how it plans to "mitigate" problems at an offshore field, Magda Chambriard, Brazil's head oil regulator, told reporters on Tuesday.

Chevron had its Brazilian drilling license suspended by the regulator, known as the ANP, after a November oil spill in the Frade field northeast of Rio de Janeiro.

(Reporting By Jeb Blount; Editing by Gary Hill)