The government, which holds 68.6 per cent interest in IOC, will sell 24.28 crore equity shares through an offer for sale (OFC) on Monday.
"... The floor price for the sale in terms of the Sebi OFS Circular shall be Rs 387 per equity share of IOC," the government said in a regulatory filing.
The price fixed is 1.8 per cent lower than Friday closing of Rs 394.45 per IOC share on BSE.
IOC's share sale will be the fourth disinvestment this fiscal, but the biggest so far in 2015-16.
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The earlier three stake sales have raised about Rs 3,300 crore.
The IOC stake sale will, however, dwarf in front of Rs 22,557 crore that the government raised through a stake sale in Coal India Ltd last year.
The government is targeting to raise Rs 69,500 crore from disinvestment in the current fiscal.
IOC is the nation's biggest oil refining and marketing company with 54.2 million tonnes of refining capacity or roughly one-fourth of India's total refining capacity of 215.1 million tonnes.
The OFS will open at 0915 hours on Monday and close on the same day at 1530 hours.
At least 20 per cent of the offer size has been reserved for retail investors, who will also get a 5 per cent discount to the cut-off price, according to the offer document.
"No single bidder other than mutual funds and insurance companies shall be allocated more than 25 per cent of the shares being offered," it said.
Retail investor has been defined as an individual investor who places bids for shares of total value of not more than Rs 2 lakh aggregate.