"A lot of short positions are being rolled over in Reliance Industries, indicating a bearish outlook," said Kunal Sukhani, manager of institutional equities at Asian Markets Securities.
The stock market, which has the heaviest weight on the main BSE index, has come under pressure following a delay in the company's plan to reach full gas output from its field off India's east coast.
The oil secretary said late on Wednesday Reliance would be able to pump natural gas at full capacity from its deep-sea field during the year to March 2013, indicating a delay of almost two years.
By 11:09 a.m., the 30-share BSE index was trading down 0.2 percent at 17,921.28 points, with 19 of its components declining.
"Market is volatile because of derivatives expiry," said Sukhani, referring to the monthly contracts on the National Stock Exchange.