Updated from 3:09 p.m. EDT

Crude oil prices fell Monday, after closing above $50 a barrel Friday for the first time in history.

The November futures contract closed down 21 cents, or 0.4%, to $49.91 in regular floor trading on the New York Mercantile Exchange. Friday's settlement price was the highest in the 21-year history of crude futures trading on the exchange. Prices are up about 14% in the past three weeks, the latest leg of a rally that started in May.

Traders are worried about short-term supplies during a period of unusually strong global demand. U.S. production in the Gulf of Mexico is still recovering from disruptions from Hurricane Ivan, while civil unrest in Nigeria has caused temporary cutbacks there as well. The government there is holding talks with leaders of a rebel group in the Niger River delta, the main source of the African nation's abundant oil reserves. Production has already been disrupted and the rebels are threatening to sabotage facilities there.

Market sentiment remains largely bullish despite efforts by OPEC to keep a lid on prices. Saudi Arabia Tuesday said it would boost its official production capacity by 1.5 million barrels to 11 million barrels a day.

The move by the world's largest oil exporter follows OPEC's decision two weeks ago to increase its official production ceiling for the third time in three months. The cartel said it was raising output by 1 million barrels a day, after boosting production by a combined 2.5 million barrels in July and August.