Mumbai, Nov. 12 -- The key equity indices traded with major gains in the mid-morning trade, supported by optimism over a potential trade agreement with the U.S. and the reopening of the American government. Investor sentiment was further buoyed after Bihar exit polls indicated a likely victory for the incumbent NDA alliance.

The Nifty traded above the 25,850 mark. Auto shares extended gains for fourth consecutive trading session.

At 11:30 ST, the barometer index, the S&P BSE Sensex, zoomed 646.31 points or 0.77% to 84,517.63. The Nifty 50 index added 191.30 points or 0.74% to 25,886.10.

In the broader market, the S&P BSE Mid-Cap index rose 0.36% and the S&P BSE Small-Cap index added 0.70%.

The market breadth was strong. On the BSE, 2,...