A flood of some 39.1 million Google shares could find their way on to the market today, potentially reducing the stock's trading price, as employees and others who were able to buy into the internet search engine's initial public offering in August take the first chance to cash-in.

Google shares have proved to be among the most fashionable tech stocks of late, and closed on Monday at $184.87. When the shares were floated, they sold at $85 each, almost half the price that the company first wanted to float at.

Before today, 27.2 million of Google's 273.4 million shares were free for trading. The number of shares available will rise ten-fold in the next three months, as lock-in conditions of the IPO expire. Two lock-up periods that each cover 24.9 million shares expire in mid-December and mid-January. In February, another 176.8 million shares are clear to go on the market.

Booming sales of advertising placed next to Google's search results have drawn investors to the California-based company, which with a valuation of $50.5 billion makes it more valuable than traditional American business giants McDonald's or Boeing.

While some institutional investors are known to have already sold their initial Google share purchases in profit-taking, some analysts suggest that the stock is ideal for long-term growth.

Google and some of its executives, including co-founders Larry Page and Sergey Brin, sold 22.6 million shares in the initial public offering on August 18.

The release of the shares comes as Google is beginning to face stiff competition in the search engine market from Yahoo! and, since last week, from Microsoft.

Both companies are competing for a share of the paid-search advertising market, which is estimated to be worth $5 billion. Yahoo's advertising sales tripled to $765.1 million in the third quarter from a year earlier.

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