Oil and Natural Gas Corporation (ONGC) plans to invest about Rs 26,000 crore in putting 50 onshore and offshore fields on production, 49 through inhouse efforts and one through service contract. ONGC's efforts to monetise these fields stem from two things - a burgeoning demand for natural gas and the absence of any significant on-land gas find. The company, which accounts for 79 per cent of India's crude oil and 54 per cent of natural gas production, said it had taken a strategic decision to improve production by early development andmonetisation of new and marginal fields.Meanwhile, ONGC, which is exploring coal bed methane (CBM) in eastern India, will relinquish one block and file product sharing contract (PSC) for four on which it has found gas in viable quantities this year. ONGC had received nine blocks in eastern India, out of which it had relinquished four earlier and was working on the rest of the blocks. These include Jharia, Bokaro, North Karanpura and Ranigunj, apart from the South Karanpura.