The government, which owns 68 percent of the company, will sell 240 million shares on Monday through a stock market auction, it said in a regulatory filing to the Bombay stock exchange.
The sale is expected to raise more than 95 billion rupees ($1.5 billion) based on the current price of the stock.
The government is seeking to raise as much as $11 billion this fiscal year by selling stakes in its string of state-run companies, in a bid to narrow the fiscal deficit.
Earlier this month, the government said it was aiming to sell a 10 percent stake in giant Coal India that experts said was valued at around $3.7 billion.
Indian Oil is the country’s largest refiner with annual sales of around $73 billion. It has outperformed the market this year, reaping the benefits of lower global crude prices.