Cairn Energy is lifting the oil sector higher after being upgraded to 'buy' from 'hold' by the broker Citigroup. The broker sees strong potential in the oil explorer's accelerated activities in Greenland.Among smaller companies, shares in oil and gas firm Aminex jumped after it announced the spudding of the Likonde-1 Well in southern Tanzania, in which it has a 37.5% interest.The well is 50% owned by Tullow Oil, with Solo Oil owning the remaining 12.5%. Both are also higher.The broader sector is lifted by crude prices at a 15-month highThe beverages sector is lacking fizz, with SABMiller lower after it pulled out of the race to buy the Femsa stable of beer brands leaving the way clear for rival brewer Heineken.Top performing sectors so far todayIndustrial Metals 5,353.82 +2.34%Oil & Gas Producers 8,595.76 +1.61%Construction & Materials 3,599.85 +1.30%General Retailers 1,723.04 +1.26%Health Care Equipment & Services 3,548.16 +1.03%Bottom performing sectors so far todayForestry & Paper 3,997.25 -2.11%Life Insurance 3,927.43 -1.77%Beverages 8,062.99 -1.30%Industrial Engineering 4,147.17 -1.20%Banks 5,022.43 -1.07%