Oil prices extended losses from the previous session on Friday and were set for a sixth straight week of declines as skepticism mounted over OPEC+ output cuts.
Investors also remained concerned that worsening economic conditions in China will dent fuel demand.
Benchmark Brent crude futures dipped 0.3 percent to $80.59 a barrel, with a weaker dollar helping cap the downside. WTI crude futures were down 0.3 percent at $75.72.
The OPEC+ group of petroleum producing nations on Thursday agreed to voluntary output cuts totaling about 2.2 million barrels per day for early next year, following a slump in crude prices and predictions of a renewed surplus next year.
There are concerns that OPEC+ might find it tough to follow through and reduce output, as the output cuts announced are voluntary and not mandatory.
Meanwhile, a private gauge of China's factory activity unexpectedly swung to expansion in November, contrasting with the official index that signaled a contraction.
The dollar slipped while Treasuries held steady as traders weighed Fed rate cut prospects.
