Benchmark oil for May delivery was down 44 cents to $106.43 at late afternoon Singapore time in electronic trading on the New York Mercantile Exchange. The contract rose $1.52 to $106.87 per barrel in New York on Friday.
Brent crude for May delivery was down 42 cents at $124.71 per barrel in London.
Crude has hovered between $105 and $110 for the last month, up from $75 in October, amid worries that a military strike by Israel or the U.S. on Iran's nuclear facilities could disrupt supplies from the oil-rich Middle East. On Friday, reports said Iran's crude exports fell sharply last month, suggesting sanctions imposed by Western powers have begun to impact that country's economy.
President Barack Obama said Sunday that there is still time to resolve the dispute over Iran nuclear program diplomatically, but that the window is closing.
"A sizable risk premium is likely to remain in place for some time while the Iranian situation goes unresolved," National Australia Bank said in a report. It "suggests that prices through 2012 will continue to sit north of $100."
Signs of tepid crude demand in the U.S. and Europe and slowing economic growth in China were weighing on prices. Analysts are also concerned higher fuel costs will undermine consumer spending and trigger inflation.
"Elevated oil prices are beginning to take a toll on emerging market economies," Morgan Stanley said in a report.
In other energy trading, heating oil was down 0.4 cent at $3.22 per gallon and gasoline futures fell 0.2 cents at $3.37 per gallon. Natural gas gained 1.4 cents at $2.29 per 1,000 cubic feet.