Mumbai, Dec. 12 -- The headline equity indices traded with substantial gains in the early afternoon trade, with the Sensex and Nifty extending the previous session's Fed-fuelled relief rally after a three-day slide. Market sentiment remained constructive ahead of key domestic inflation data due later in the day.

The Nifty traded above the 26,000 level. Oil & gas shares advanced after declining in the past trading session.

At 12:30 ST, the barometer index, the S&P BSE Sensex, surged 420.22 points or 0.49% to 85,235.24. The Nifty 50 index added 124.40 points or 0.48% to 26,022.80.

In the broader market, the S&P BSE Mid-Cap index jumped 0.74% and the S&P BSE Small-Cap index advanced 0.47%.

The market breadth was strong. On the BSE, 2,412...