Unsurprisingly, there were only two categories making gains on Tuesday, as markets worldwide suffered a broad sell-off on the back of the ongoing debt crisis in Europe.In London, the oil equipment, services and distribution sector was among the worst performing groups of stocks in the afternoon as Brent crude dropped below the psychologically important $100 level. By 15:31, the price had sunk 1.75% to $99.93.Goldman Sachs has scaled back its forecasts for Brent crude prices for 2012 from $130 to $120 a barrel, saying that economic headwinds in Europe will hit demand.International engineering and project management company AMEC was trading nearly 7% lower, despite the announcement yesterday that it had been awarded a Front End Engineering Design (FEED) contract for GDF SUEZ E&P UK's Cygnus gas field development in the North Sea. Oilfield services firm Wood Group and well construction group Hunting also plummeted on the FTSE 250.Meanwhile, the food and drug retailers were in demand, with supermarket giant Tesco leading the rise.Tesco was among the few stocks posting gains on the FTSE 100 ahead of its interim results due tomorrow, after UBS upgraded the stock from neutral to buy and added the stock to its 'Key Calls' list, highlighting that "driving higher returns is now at the heart of group strategy." Morrisons rose in sympathy. BCTop performing sectors so far todayFood & Drug Retailers 4,366.05 +1.17%Alternative Energy 8,854.28 +0.69%Bottom performing sectors so far todayAutomobiles & Parts 3,624.00 -7.74%Industrial Metals & Mining 3,992.98 -7.14%Oil Equipment, Services & Distribution 17,689.28 -6.30%Life Insurance 3,199.36 -5.99%Electronic & Electrical Equipment 2,251.90 -5.95%