Oil deepened its weekly decline as Goldman Sachs Group said a global supply surplus could force prices to $20 a barrel. Futures fell after two weeks of gains. Goldman said yesterday the world’s oil glut is even bigger than it thought.

Speculators cut bullish bets on oil to the lowest level since March because an agreement over Iran’s nuclear programme threatens to prolong a global supply glut.

Oil fell in 2014 by the most since the 2008 global financial crisis as US producers and the Organisation of Petroleum Exporting Countries ceded no ground in their battle for market share amid a supply glut.