Oil prices surged as much as 5 percent on Thursday, with Brent crude at its highest in about 16 months, extending gains after OPEC and Russia agreed to restrict output to reduce the global supply glut more quickly. The Organization of the Petroleum Exporting Countries agreed on Wednesday to its first oil output reduction since 2008 after de-facto leader Saudi Arabia accepted “a big hit” and dropped a demand that arch-rival Iran also slash output. The deal also included the group’s first coordinated action with non-OPEC member Russia in 15 years. On Thursday, Azerbaijan said it was also willing to engage in talks on cuts. Doubts about the historic deal were widespread in the market. “It remains to be seen how well they stick to the plan, but if OPEC hadn’t come to an agreement the probability is that oil prices would have fallen to $40 a barrel, perhaps even lower,” said Simon Flowers, chief analyst at consultancy Wood Mackenzie. The OPEC deal triggered frenzied trading, with Brent futures hitting record trading volumes for February and March, when the supply cuts should start to be visible in the market.