Global crude oil prices sold-off again, today. Brent crude oil futures slumped to an over four-year low of 71.12 dollars a barrel. U.S. crude oil also dropped to an over four-year low of 67.75 dollars a barrel. Oil tumbled after the Organization of Petroleum Exporting Countries yesterday decided not to cut output, a move that could leave oil markets heavily oversupplied. Saudi Arabia blocked calls from other members of the OPEC for output reductions. Some analysts said Saudi Arabia and OPEC may no longer be the mechanism to balance the market. Instead, in a fundamental change, prices will be the mechanism to rebalance the market. Brent has lost more than a third of its value since June, as increasing shale output in North America has helped create an oil glut at a time of sluggish global economic growth. Russia's most powerful oil official, Igor Sechin said oil prices could fall to 60 dollars or below by the end of the first half of next year.