NEW YORK (CNN/Money) - Oil prices touched their lowest levels in two months Monday on anticipation that supplies will build further as OPEC keeps the taps wide open.

Light crude for December delivery lost 45 cents, or nearly 1 percent, to close at $46.87 on the New York Stock Exchange, after falling to as low as $45.40 -- the lowest level since oil closed at $45.59 a barrel on September 17.

In London, Brent crude dropped $1.97 to $40.34 a barrel.

A rebound in crude oil inventories in the United States, the world's largest energy market, has brought oil prices down from record highs.

Supplies have risen 22 million barrels in the past seven weeks, thanks in part to the highest OPEC production in decades.

"I expect another build in crude this week," said Richard Mueller, oil analyst at research firm Energy Security Analysis, referring to the report from the Energy Information Agency due Wednesday.

"OPEC is pumping incredible amounts of oil, and a lot of it is steaming this way."

The increase in inventories has knocked more than 18 percent off the intraday trading high of $55.67 hit a few weeks ago.

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"Given that the key factors driving bearish sentiment -- high crude imports and a lack of sharply colder weather to cause a jump in U.S. heating oil demand -- show no immediate signs of changing, prices will continue their downward trend," consultants PFC Energy told clients, according to Reuters.

Prices fell Monday as easing tensions to a potential oil strike in Nigeria countered news that saboteurs had set several oil installations on fire in Iraq.

With crude prices on a downward slide, Mueller noted that OPEC, and Saudi Arabia in particular, will be watching its output closely. "If prices continue to fall at this pace, you might see them start to hit the brakes, but we're not there."