Facebook’s valuation has been all over the map. In 2007, a $240 million investment from Microsoft pegged the company at a whopping $15 billion. After Wall Street imploded, the company plummeted to $3.7 billion in its own estimation, according to court documents discovered by the AP in February of this year. By May it climbed back to $10 billion with an investment from Russian investment firm Digital Sky Technologies. DST then offered to buy up to $100 million in common stock from shareholders at a $6.5 billion valuation in July.

Since then, the company has posted strong numbers, topping 300 million users and declaring itself cash-flow positive in September.

This week, Facebook climbed up back up to a respectable position. On Thursday, SecondMarket, an exchange that allows sophisticated investors to buy private company stock, told Bloomberg that Facebook shares are selling for $21 on the site, giving the company a $9.5 billion valuation. That’s a 42% jump from the going price in July. SecondMarket spokesman Mark Murphy said there have been about a dozen transactions of Facebook shares in the last 60 days, the most recent occurring last week.

On SharesPost, another private company stock exchange, buyers have offered $20 for Facebook shares, up 35% from 3 months ago. SharesPost said the last transaction on the site was 15,000 shares sold for $12 each in August.

IPO?

Any news about Facebook is fuel for the IPO rumor mill. Paul Bard, a Renaissance Capital analyst, told Bloomberg, "The fact that the stock on these private exchanges moved - I'm sure that has to do with the fact that people think a deal is coming sooner rather than later."

Lise Buyer, who helped run Google’s IPO disagrees. She cites the company’s recent decision to allow employees liquidity just a few months ago. If an IPO were immanent, the argument goes, a company wouldn’t make the potentially embarrassing move of letting employees sell. The higher price simply means that investors who can hang on for a while think that when an IPO does happen, it’ll be at a higher price than the last round paid.