The Bombay Stock Exchange benchmark Sensex closed flat after a sharp plunge in Reliance Industries, triggered by reports of poor gas find in one of its wells, erased early gains.

The 30-share benchmark Sensex, which gained 217.03 points in the morning, closed 21.07 points up at 16,810.81.

The wide-based National Stock Exchange index Nifty shuttled between 5,054.95 points and 4,983.25 points, before closing with a gain of 8.45 points at 4,997.05.

Sensex-heaviest Reliance Industries tumbled over four per cent, or by Rs 86.25, to Rs 2,047.30 after one of its partners, Britain's Hardy Oil and Gas, said that it is abandoning work on an exploratory well in a Krishna Godavari basin block owing to poor gas find.

In the 30-share BSE index, 18 scrips closed with gains, while 12 ended lower, led by RIL, Reliance Infra, RCom, Tata Motors and Tata Steel.

However, a weakening market was capped on reports of a better closing in Asian stock markets and a higher opening in the Eruopean stocks this afternoon.