Chinese customs authorities are stepping up inspection checks on cargoes of heavy crude oil after uncovering several Iranian shipments that were mislabelled as diluted bitumen in an effort to bypass import quotas.
Oil prices fell on Monday as jitters over the prospect of the U.S. Federal Reserve raising interest rates, which could slow growth and hit fuel demand, and worries about weaker Chinese manufacturing data combined to erase earlier gains.
Saudi Arabia's stock market ended higher on Sunday in response to Friday's rise in oil prices, while the Egyptian index was in the red on profit-taking.
Oil prices posted mild gains on Friday, but headed for a second week of declines as disappointing U.S. economic data and uncertainty over further interest rate hikes weighed on the demand outlook.
Oil prices rose slightly on Thursday, finding some support after heavy losses in the previous two sessions that were driven by fears of a U.S. recession and an increase in Russian oil exports which dulled the impact of OPEC production cuts.