BP, BG and Wood Group were among the best performers on the FTSE 100 on Wednesday afternoon, providing a boost to the oil and gas producing sector.Drilling in the previously untested northern segment of the Mad Dog field in the Gulf of Mexico has resulted in a "significant resource extension", according to the oil giant BP.BG Group, too, was a high riser on news that it is in discussions to buy Indian firm Oil & Natural Gas Corp (ONGC). BG India's president and managing director said, "We had given a proposal to ONGC a while back. The ball is in their court."Sector peer Wood Group was in demand, with Reuters saying that the rise may have to do with worries that the stock may be relegated out of the top share index during the quarterly review due after the closing of trading.Tullow Oil, Petrofac and Essar Energy were also registering gains, as Brent crude rose 1.5% to $114.64 a barrel by 15:39. Just two sectors were in the red, one of them being the tobacco sector, which is made of just two stocks, British American Tobacco (BATS) and Imperial Tobacco (IMP).While BATS was edging higher, IMP offset these gains after Goldman Sachs downgraded it from buy to neutral. The cigarette maker was removed from the stockbroker's pan-European buy list and downgraded it target price from £24 to £21.90. Shares were 2.14% lower at 2,060p.BCTop performing sectors so far todayIndustrial Metals & Mining 5,886.41 +5.69%Automobiles & Parts 4,390.89 +5.56%Personal Goods 21,580.49 +4.27%Technology Hardware & Equipment 689.10 +4.16%Oil & Gas Producers 7,490.11 +3.76%Bottom performing sectors so far todayFood & Drug Retailers 4,354.92 -0.49%Tobacco 31,264.24 -0.31%