Oil markets opened cautiously on Tuesday, with many traders reluctant to take on large new positions ahead of the G20 gathering in Argentina this weekend and the OPEC meeting in Austria next week.
U.S. West Texas Intermediate (WTI) crude futures were at $51.52 per barrel at 0011 GMT, down 11 cents, or 0.2 percent from their last settlement.
International Brent crude oil futures had yet to trade, but had barely hung on to $60 per barrel at the end of the previous day after Friday's price plunge.
Since their most recent peaks in early October, oil prices have lost almost a third of their value, weighed down by an emerging supply overhang and by widespread weakness in financial markets.
"The recent weakness seems ... to have been driven by a wider impending sense of doom amidst weak equities, geopolitics, subsequent softening demand and increasing supply," said Jack Allardyce, oil analyst at financial services firm Cantor Fitzgerald Europe.
Looking ahead, Allardyce said "a lot depends" on the outcome of the Group of 20 (G20) meeting in Buenos Aires where the United States and China are expected to address their trade disputes, and on a meeting of the Organization of the Petroleum Exporting Countries (OPEC).
The leaders of the G20 countries, which make up the world's leading economies, are due to meet on Nov. 30 and Dec. 1, with the trade war between Washington and Beijing top of the agenda.
OPEC's 175th annual meeting takes place at its headquarters in Vienna on Dec. 6, and the group will discuss its output policy together with some non-OPEC producers, including Russia.
"It looks as though the market has already decided that the mooted 1.4 million barrels of oil per day cut to output isn't enough to offset the decline in demand growth projections, so if that is the number then the current (oil price) level could remain into the new year, or we might see some more weakness," Allardyce said.