Oil prices tumbled Friday, plumbing five-year lows, following an OPEC decision that will likely translate into a lingering glut of crude. Brent crude, the global benchmark, fell $2.43, or 3.4%, at $70.15 a barrel on ICE Futures Europe, its lowest settlement since May 2010. Friday’s selloff added to losses on Thursday, a regular trading day in Europe, when Brent plunged 6.7% to settle at its lowest level since August 2010. It also dipped below $70 a barrel in intraday trading for the first time since May 2010.