Brent crude oil slipped further into the red on Friday afternoon, falling below $60 a barrel as a stronger dollar balanced worries over the impact of fighting in Libya and Iraq on Middle East and North African oil production.
U.S. light crude closed down $1.15, or 2.27 percent, at $49.61 a barrel. Brent was down 65 cents a barrel at $60.
The dollar hit an 11-½-year high against a basket of currencies on Friday after strong U.S. jobs data boosted expectations of a sooner-than-expected interest rate rise in the world's largest economy.
U.S. employment accelerated in February and the jobless rate fell to 5.5 percent, signs that could encourage the Federal Reserve to raise interest rates in June.
Oil services company Baker Hughes reported the number of U.S. rigs exploring for oil fell by 63 in the last week, up from a 33-rig decline in the previous survey. The report is an indicator used by some investors to gauge whether shale producers are cutting output after prices slumped.