The Board of state-owned Oil and Natural Gas Corp ( ONGC ) Thursday approved buyback of 25.29 crore shares for Rs 4,022 crore as part of the government plan to get cash-rich PSUs to part with their surplus.The government, which holds 65.64 per cent stake in the company, stands to gain about Rs 2,640 crore from tendering some of its shares in the buyback programme.In a regulatory filing, ONGC said its board of directors approved "buyback of equity shares of the company not exceeding 25.29 crore being 1.97 per cent of the total paid-up equity shares of the company at the price of Rs 159 per equity share payable in cash for an aggregate consideration not exceeding Rs 4,022 crore".This follows government pushing cash-rich PSUs to use their funds to buy back shares or pay a higher dividend. The government is looking to bridge budgetary deficit through higher receipts of dividend as well as selling its shares in PSUs in the buyback programmes.ONGC will, however, not pay an interim dividend for now as it is left with almost no surplus after accounting for its capital expenditure, sources with knowledge of the development said.ONGC shares closed almost flat at Rs 148.65 on the Bombay Stock Exchange (BSE) Thursday.Stock buybacks refer to the repurchasing of shares by the company that issued them. A buyback occurs when the issuing company pays shareholders the market value per share and re-absorbs that portion of its ownership that was previously distributed among public and private investors.Earlier this month, state-owned Indian Oil Corp (IOC) said it will buy back 29.76 crore shares for about Rs 4,435 crore and spend another Rs 6,556 crore on paying an interim dividend to shareholders.The board of the country's largest oil firm, IOC approved buyback of up to 29.76 crore equity shares, or 3.06 per cent, at Rs 149 per share.Besides ONGC and IOC, at least half a dozen other central PSUs have disclosed share buyback programmes. Prominent among these include NHPC, Coal India, Oil India Ltd, BHEL, NALCO, NLC, Cochin Shipyard, and KIOCL.The government is expected to participate in each of the share buyback programme of these PSUs with anticipation of netting over Rs 5,000 crore.IOC had also declared an interim dividend of 67.5 per cent or Rs 6.75 per share for fiscal 2018-19. The total dividend payout, excluding tax, would be Rs 6,556 crore, of which the government will get Rs 3,544 crore plus the dividend distribution tax.Last month, Oil India Ltd announced a buyback of 5.04 crore of its share for a little over Rs 1,085 crore.The Department of Investment and Public Asset Management (DIPAM), which has been set a target to raise Rs 80,000 crore for the government through stake sale in central public sector enterprises, had prodded all cash-rich PSUs to go for share buybacks.PSUs having a net worth of at least Rs 2,000 crore and a cash balance of more than Rs 1,000 crore have to mandatorily go in for share buyback.Of the Rs 80,000 crore disinvestment target, the government has so far raised just over Rs 15,000 crore through minority stake sale in PSUs.