ANSWER: ONGC
Explanation:
Benchmark BSE Sensex rose rapidly by 858 points during the first week of October causing 9 of the top 10 most valued companies to gain INR 80,086.27 crore in market cap. ONGC posted the biggest gains. Sensex surged to 27,079.51, second straight weekly rise. Apart from Infosys, top 9 companies which saw market valuation rise included ITC, RIL and TCS. M-cap of ONGC surged to INR 2,25137.72 crore from INR 26,393.68 crore. TCS topped the list of companies being followed by RIL, ITC, HDFC Bank, Infosys, ONGC, Sun Pharma, CIL, HDFC and SBI.