Oil prices tumbled after a meeting by major exporters in Qatar collapsed without an agreement to freeze output , leaving the credibility of the OPEC producer cartel in tatters and the world awash with unwanted fuel.<br />Tensions between Saudi Arabia and Iran were blamed for the failure which revived industry fears that major government-controlled producers will increase their battle for market share by offering ever-steeper discounts.<br />Oil prices have fallen by as much as 70 percent since mid-2014 as producers have pumped 1 to 2 million barrels of crude every day in excess of demand.
