Oil prices fell on Monday after the long Christmas weekend, with U.S. crudes defending a newly gained premium over internationally traded Brent contracts in quiet trading ahead of the end of the year. Front-month U.S. West Texas Intermediate (WTI) futures were trading at $37.87 per barrel at 0311 GMT, down 23 cents from their last settlement. Brent was down 16 cents at $37.73 a barrel, meaning that U.S. crude defended a premium it gained over the globally traded benchmark last week.