Oil prices crashed below 50 dollars a barrel on Thursday as plunging equities and weak US data sparked fresh fears that a worldwide recession would ravage energy demand. In New York, light sweet crude for delivery in December plunged 4.00 dollars a barrel to close at 49.62. The December contract expired at the close after hitting an intraday low of 48.64 dollars, a level last seen in May 2005. The contract had not been below the 50-dollar level since January 18, 2007.