The price of oil slipped 1.6% on Monday as dealers anticipated a government report would show another increase in US crude inventories as the economic slowdown hits fuel consumption.
Energy analysts expect the US Energy Information Administration's weekly report due on Wednesday on petroleum inventories to show the fifth straight increase in crude stockpiles as weak demand and robust imports pad storage.
US crude fell 74 cents to settle at $US45.73 a barrel, after rising to a session high of $US48.59.
London Brent dipped $US1.41 to $US46.96 a barrel.
The losses were tempered by evidence OPEC was complying with the bulk of its output cut agreements as the cartel struggles to stabilize a market that has dropped more than $US100 since July's peak.
The Organization of the Petroleum Exporting Countries has agreed to cut some 4.2 million barrels of daily output since September, but questions remain about whether the cuts will be enough to offset shrinking demand.