More than four out of 10 web searches conducted in the US are now done using the Google search engine, figures show.
Google's share rose to 42% in February, up 6% on the same month in 2005, while rival Yahoo saw a 4% drop to 27%, according to tracking firm ComScore.
Usage of MSN's search engine fell by 3% to 13% said ComScore, while Ask had a 1% rise to 6%.
In a separate report, analysts Merrill Lynch said Google's advertising revenues was expected to rise.
The Merrill Lynch report said: "We expect Google's increased market share in search queries, and better monetisation of queries to lead to increased share of ad dollars relative to its competitors."
A report by RBC Capital Markets said Google could go on to capture a 70% market share.
It said: "The question really comes down to how long it could take."
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ComScore said the total number of search queries rose by 11% over the year.
Google share prices rose by 1.4% after ComScore's results were announced on Tuesday, rising to $374.77 (£216), while Yahoo rose 1.5% to $31.93 (£18.40).
Earlier this month, Google chief executive Eric Schmidt reiterated the firm's belief that it will continue to enjoy strong increases in its revenues.
He spoke out two days after his chief finance officer George Reyes warned revenues were slowing, prompting a 10% dip in the share price.
A federal judge ordered Google to turn over search data, including 50,000 web addresses, to the US government as part of the authorities' bid to prevent access to online pornography.
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