(VOVworld) - Crude oil prices have increased by nearly USD 4 a barrel over a record decline in the number of oil drilling rigs in the United States.

A pumpjack brings oil to the surface in the Monterey Shale, California, April 29, 2013

On Friday, the US benchmark West Texas Intermediate (WTI) for March delivery suddenly soared to over USD 48.24, up USD 3.71 from the day before. European benchmark Brent crude for March also followed a similar pattern, trading at USD 52.99 a barrel, a gain of USD 3.46.  Some observers argued that short-covering by big investors on the final trading day of January was likely responsible for the unexpected rise in oil prices.