Employees and early investors in the world's most popular web search engine, Google, will be able to sell 39 million shares from Tuesday.
Restrictions were imposed ahead of its flotation in August, to prevent shares being dumped quickly onto the market.
In one of the most closely-watched initial public offerings in stock market history, the US-based company sold 19.6 million shares at $85 each.
Since then, they have risen to more than $185 apiece.
The restriction - known as a lockup - is being eased piecemeal: in all, some 227 million additional shares will become free to trade by February 2005.
The sales could make many of Google's workers into millionaires.
There are fears that any potential increase of shares in circulation from Tuesday may ease demand for stock.
However, analysts say shareholders will hold back from selling all their shares immediately, and Google's good performance means demand will hold.
"Given how strong Google's fundamentals are, you could say there will be demand to sop up what's sold," Mark Mahaney, an analyst at American Technology Research, told Reuters news agency.
"The outcome here could be a potential ceiling for the stock price in coming months, rather than downward pressure," Morgan Stanley analyst Mary Meeker said, Reuters reported.
In its first earnings report since floating on the stock market, Google said it made a net profit of $52m in the three months ending 30 September.
Sales surged to $805.9m in the third quarter, up from $393.9m a year earlier.
Google's main service - its internet search - is free to users, so the firm makes much of its money from selling advertising space linked to the words for which its users search.
It also sells the use of its technology to companies who need to make either their websites, or their internal information systems, searchable.
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