The company reported a net profit of 55.63 billion rupees for its fiscal third quarter ended December, down from 67.4 billion rupees a year earlier, which had included a one-time gain on account of royalty dues from a joint venture partner.
Analysts on average had expected the company to post a net profit of 53.7 billion rupees for the quarter, according to Thomson Reuters Starmine data.
Net sales rose 16 percent to 209.87 billion rupees.
Shares of ONGC, India's third-biggest company by market value, closed 1.7 percent lower on Monday, ahead of the results. The stock has jumped 15 percent so far in 2013, outperforming a 6 percent rise in the sectoral index.