Facebook said in a regulatory filing Wednesday that about 421 million shares will be sold, up from 337 million under its earlier plans.
The increased size signifies heavy investor demand for the shares. The news comes a day after Facebook raised the expected price range for the stock to a range of $34 to $38 per share, up from its previous range of $28 to $35.
If all the shares being offered -- including more than 63 million more shares that the deal's underwriters can sell to cover excess demand -- are sold at the high end of the expected price range, the social network's offering could raise more than $18.4 billion. That would make Facebook one of the biggest IPOs ever.
The IPO is the most hotly anticipated in years and would value Facebook overall at more than $100 billion.
In a filing with the Securities and Exchange Commission, Facebook says that the extra shares being made available are coming from its current shareholders. The selling shareholders are now offering approximately 241 million shares, up from about 157 million shares previously.
Facebook will not receive any proceeds from the stock sold by the selling shareholders.
The regulatory filing also disclosed that CEO Mark Zuckerberg will control about 55.8 percent of the voting power of the company's outstanding capital stock following the offering. This is down slightly from the 57.3 percent he was initially expected to have.
Facebook has more than 900 million users who log in at least once a month.
Morgan Stanley leads the team of 33 underwriters selected for the Facebook offering, followed by JPMorgan Chase and Goldman Sachs.
The offering is expected to set the final price Thursday evening. Shares would start trading on the Nasdaq on Friday under the "FB" ticker symbol.