Global crude oil prices shot up 13 percent today, after Organization of the Petroleum Exporting Countries (opec) and Russia cut a deal to reduce output to drain a global supply glut. Brent crude oil futures surged 13 percent to 52.54 dollars a barrel. US crude jumped to 50.11 dollars a barrel.OPEC yesterday agreed to its first oil output reduction since 2008, after Saudi Arabia dropped a demand that Iran also slash output. The cut of 1.2 million barrels per day was at the upper end of expectations. But some doubts over the output cut remain.British bank, Barclays said the agreement is to cap production levels, not export levels. US bank, Morgan Stanley said skepticism remains on individual countries' follow-through on the cut.Analysts also said, other producers could fill the gap. And Goldman Sachs said it expects oil prices to average just 55 dollars per barrel in the first half of next year.