Oil prices were up about 1 percent on Monday after comments by Iran's leader exhorting the need for other oil producers to join OPEC in supporting the market.
Iran's President Hassan Rouhani told his Venezuelan counterpart Nicolás Maduro in a telephone conversation that it was essential for oil producing countries to take a decision to raise the price of oil and stabilize the market, Tehran state news agency IRNA reported.
Rouhani's remarks added to the bullish fervor in the market since last week after the Organization of the Petroleum Exporting Countries announced its first planned output cut in eight years.
December Brent crude futures were last up 62 cents, or 1.2 percent, at $50.81 a barrel by 3 p.m. (1900 GMT), retreating from a six-week high of $50.90.
U.S. West Texas Intermediate (WTI) settled up 57 cents, or 1.2 percent, at $48.81 a barrel. It earlier hit $49.02, its highest since July 5.