India's largest oil and gas producer ONGC will this year reverse years of decline in production and gradually raise output thereafter, as it invests billions of dollars to produce from newer discoveries, a top company official said. Oil and Natural Gas Corporation (ONGC) in fiscal 2021-22 produced 21.707 million tonne of crude oil, which is refined to produce petroleum products like petrol and diesel, and 21.68 billion cubic metre (bcm) of natural gas, which is used to produce electricity, manufacture fertiliser and as CNG in automobiles.