Detroit ? Investor demand for General Motors stock has been so strong that the company will expand its initial public offering by 31 percent, to 478 million common shares, a person briefed on the sale said Tuesday.

The move, coupled with an expected stock price of $33 per share, brings the U.S. government closer to getting back the $50 billion it spent bailing out GM last year. But depending on how GM performs in the next few years, taxpayers could still come up short.

If the government sells 412 million shares for $33 each, it will get $13.6 billion. It will still have about 500 million shares, or about 33 percent of GM. It would have to sell them for about $53 a share, or $26.4 billion, for taxpayers to get their $50 billion back.

The increased number of shares could make GM’s IPO on Thursday the largest in history for a U.S.-based company. If GM’s sale of preferred shares is included, the offering could have a total value of over $22 billion, topping Visa Inc.’s $19.7 billion IPO in 2008, according to the IPO tracking firm Dealogic. It could even surpass Agricultural Bank of China’s $22.1 billion offering in July to become largest IPO in the world.

Demand for GM stock was so heavy that GM’s bankers stopped taking orders for the sale on Tuesday afternoon after essentially running out of shares to sell, according to the person, who asked not to be identified because he is not authorized to speak publicly about the sale.