Following strong indications from US markets and a relative fall in global crude oil prices, Indian stock indices extended their advances for the fourth straight day on Wednesday. At 9.44 am, the Nifty was trading at 17,576.00 points, up 89.05 points or 0.51 percent, while the Sensex was trading at 59,273.77 points, up 313.17 points or 0.53 percent.