Oil and gas firms have fallen back in spite of a rise in crude prices after the United Arab Emirates' central bank said it would take measures to protect its lenders against any potential default by Dubai World.Crude climbed above $76 in New York, but oil stocks are lower, including giants BP and Shell, in line with general nervousness in the equity markets.Cairn Energy, up 1%, is higher though after saying it is to make Capricorn a wholly owned subsidiary by buying out minority shareholder Dyas BV.Cairn is acquiring Dyas's 9.99% stake in the exploration focused Capricorn for$95m, to be satisfied through a mixture of newly issued shares and cash.The tobacco sector is posting moderate gains as Imperial advances, though British American falls back. Top performing sectors so far todayForestry & Paper 3,576.09 +1.22%Tobacco 22,664.42 +0.13%Personal Goods 10,364.67 +0.04%Chemicals 4,370.19 +0.02%Bottom performing sectors so far todayLife Insurance 3,833.67 -1.77%Real Estate 1,971.83 -1.76%Industrial Engineering 3,731.41 -1.58%Fixed Line Telecommunications 1,998.47 -1.52%Oil & Gas Producers 7,890.85 -1.43%