European benchmark Brent oil briefly sank under $ 50 yesterday for the first time since 2009. However, prices later recovered following mixed demand signals in the United States.In morning London deals, Brent North Sea crude for delivery in February dived to another 5.5-year low at $ 49.66 a barrel, last seen in late April 2009. However, it quickly rebounded back above the 50-mark and stayed there following data showing that US crude stocks dropped by 3.1 million barrels to 382.4 million in the week ending January 2.Brent crude for delivery in February ended the day with a gain of 4 cents to $ 51.14. US benchmark West Texas Intermediate for February gained 78 cents to $ 48.75 in midday trading in New York, having already collapsed under the symbolic 50-level on Monday.