LONDON (AFP) - Oil prices sank this week to three-and-a-half-year lows close to 50 dollars a barrel, prompting the OPEC exporters' cartel to call an emergency meeting to discuss a mooted output cut. Commodity markets took a heavy knock as recession swept across the world's advanced economies, with the eurozone, as well as Italy and Germany, all recording two straight quarters of negative economic growth. "We believe the depth and duration of the current economic downturn will sustain downward pressure on metal and energy prices into 2009," said Deutsche Bank analyst Michael Lewis. "We view any recovery in commodity prices, and specifically energy and metal prices, as a 2010 event." OIL: The price of crude oil fell sharply as the International Energy Agency warned that global energy demand was being severely crimped by the effects of approaching worldwide recession. Brent North Sea crude for delivery in December on Thursday dived to 50.60 dollars a barrel " the lowest level since May 2005. At the same time, New York's light sweet crude for December delivery slid to 54.67 dollars, a level last seen in January 2007. Crude prices have collapsed by about two-thirds since striking record peaks above 147 dollars in July, on concern that a prolonged global recession could slam the brakes on energy demand. That, in turn, has sparked alarm among the OPEC cartel, whose member nations pump 40 percent of the world's crude supplies, because their oil revenues have been slashed. OPEC will hold a special meeting in Cairo on November 29, a spokesman for the organisation said on Friday amid some pressure in its ranks, notably from Iran, for a new output cut to hold up prices. The Organization of Petroleum Exporting Countries (OPEC) agreed in October to reduce production by 1.5 million barrels a day from November 1, but prices have continued to slide since then. Iran, number two oil producer in OPEC after Saudi Arabia, said it would support a decision to cut production by the cartel at the meeting. On Thursday, the International Energy Agency (IEA) slashed its 2009 oil price forecast to 80 dollars from 110 dollars, saying imminent recession was strangling demand in rich countries and crimping emerging economies. The IEA made further big cuts to its estimates of global demand growth in its monthly report but said that despite recent heavy price falls to the 60-dollar range, prices on futures contracts still hovered around 85 dollars a barrel. By Friday on the New York Mercantile Exchange (NYMEX), light sweet crude for delivery in December fell to 57.58 dollars a barrel from 62.96 dollars a week earlier. On London's InterContinental Exchange (ICE), Brent North Sea crude for January dropped to 55.34 dollars a barrel from 58.80 dollars. PRECIOUS METALS: Gold prices rose, while silver, platinum and palladium all fell. Gold "is beginning to regain its resilience as a safe-haven asset," said Helen Henton, head of commodity research at Standard Chartered. On the London Bullion Market, gold rose to 747.50 dollars an ounce at Friday's late fixing from 735.25 dollars a week earlier. Silver fell to 9.33 dollars an ounce from 10.41 dollars. On the London Platinum and Palladium Market, platinum slipped to 845 dollars an ounce at the late fixing on Friday from 849 dollars a week earlier. Palladium decreased to 216 dollars an ounce from 227 dollars. BASE METALS: Copper and aluminium prices slid to three-year lows. Copper later fought back as investors hunted for bargains and the base metal ended the week higher. "In the last few weeks there has been a significant deterioration in the physical base metal markets as the credit crunch has rapidly spread from the financial sector to the wider economy," said Henton. "Orders have dropped sharply, layoffs have accelerated and fabricating plants have been mothballed," she added. Copper on Thursday struck 3,515 dollars a tonne, the lowest level since September 2005. The same day aluminium dropped to 1,903 dollars a tonne, last seen in October 2005. By Friday, copper for delivery in three months had risen to 3,815 dollars a tonne on the London Metal Exchange from 3,785 dollars a week earlier. Three-month aluminium fell to 1,922 dollars a tonne from 1,990 dollars. Three-month lead slipped to 1,375 dollars a tonne from 1,400 dollars. Three-month zinc gained to 1,185 dollars a tonne from 1,109 dollars. Three-month tin slid to 14,020 dollars a tonne from 14,812 dollars. Three-month nickel increased to 11,274 dollars a tonne from 11,200 dollars. COCOA: Cocoa futures rose in London and steadied in New York. "This is partly due to commodity specific factors, such as the chequered start to the cocoa season in Ivory Coast which is disrupting the flow of beans for exports," said Henton of Standard Chartered. By Friday on LIFFE, London's futures exchange, the price of cocoa for delivery in March climbed to 1,357 pounds a tonne from 1,270 pounds a week earlier. On the New York Board of Trade (NYBOT), the December cocoa contract was virtually unchanged at 1,945 dollars a tonne from 1,946 dollars. COFFEE: Coffee prices advanced on both sides of the Atlantic. By Friday on LIFFE, Robusta for delivery in January increased to 1,817 dollars a tonne from 1,739 dollars a week earlier. On the NYBOT, Arabica for March gained to 115.05 US cents a pound from 112.45 cents. SUGAR: Sugar prices dropped in line with crude oil prices. Sugar is used in the production of ethanol, a cheaper alternative to motor fuel which is refined from crude oil. When crude futures fall, demand for ethanol wanes. By Friday on LIFFE, the price of a tonne of white sugar for delivery in March slid to 321.40 pounds from 339.80 pounds the previous week. On NYBOT, the price of unrefined sugar for March decreased to 11.51 US cents per pound from 12.21 cents. GRAINS AND SOYA: Grains and soya prices were mixed. By Friday on the Chicago Board of Trade, maize for delivery in December fell to 3.74 dollars a bushel from 3.75 dollars the previous week. January-dated soyabean meal " used in animal feed " dropped to 8.87 dollars from 9.21 dollars. Wheat for December rose to 5.36 dollars a bushel from 5.21 dollars. RUBBER: Malaysian rubber prices continued to climb after the commodity's top producers " Thailand, Malaysia and Indonesia " moved recently to cut production. On Friday, the Malaysian Rubber Board's benchmark SMR20 rose to 176.50 US cents a kilo from 175.25 cents a kilo a week earlier.