New Delhi, Aug. 6 -- India's plan to sell more shares in its insurance giant was no secret. But the government surprised the market by how much it raised and the pace of the deal.

Keeping details closely held until the final hours-even from some advisers-and moving quickly allowed the government to more than double its offer for sale (OFS) of Life Insurance Corp. of India (LIC) shares, raising $3.3 billion. That's the nation's biggest secondary offering through a stock exchange.

Officials in the state divestment department kept the LIC OFS launch date a secret to prevent traders from taking positions ahead of the sale and pushing the stock lower before the government could sell its shares, according to people familiar with the matter. E...