State-owned gas firm Gail (India) Ltd on Thursday reported a 58 per cent increase in its net profit to Rs 531.03 crore in the quarter ended March 31, 2003, as opposed to Rs 336.02 crore profits in the same period last year.Sales rose 15 per cent to Rs 3,077.44 crore in January-March from Rs 2,683.88 crore in the corresponding quarter of the previous fiscal, a press statement said. According to provisional figures, turnover for the year 2002-03 reached a record Rs 11,771 crore against Rs 10,573 crore in 2001-02. Net profit increased to Rs 1,607 crore in 2002-03 against Rs 1,186 crore in 2001-02. Natural gas continues to constitute the core business of Gail.