West Texas Intermediate dropped to $59.88 per barrel at 1930GMT, its lowest point since July 2009.
Meanwhile, the global benchmark Brent crude oil price is at $63.68, after it had fallen below the $64 mark on Wednesday, when the Organization of the Petroleum Exporting Countries reduced its forecast for crude oil demand for 2015 in its report.
In its Monthly Oil Market Report for December, the oil cartel reduced its forecast for crude oil demand in 2015 by 300,000 barrels per day to 28.92 million barrels per day, OPEC said in a report.
OPEC also decided not to cut production at its meeting on Nov. 27, stating that it will produce 30 million barrels of crude oil for the first half of 2015.
The steep decline in oil prices continues since June, as global oil demand remains low and there is a glut of oil supply in world markets.
While Asian and European economies are flat, the increasing value of U.S. dollar, to which crude oil prices are pegged, hampers the purchasing power of oil importing countries, and thus reduces demand.
In addition, U.S. domestic oil production is on a steady rise since the country's shale oil revolution in 2008, increasing the global supply.
Since the shale boom in 2008, U.S. domestic oil production has increased from 1.8 billion barrels in 2008 to 2.7 billion barrels in 2013, according to the U.S. Energy Information Administration.