The release last week of betas of Chrome for Mac OS X and Linux pushed the Google browser's share past Apple 's Safari and into the No. 3 spot, a Web measurement company said today.

Google shipped betas of Chrome for Mac and Linux on 8 December. Prior to that, only rougher, less stable "developer" builds were available to users.

According to Net Applications, which tracks the browser habits of 160 million unique visitors each month to the 40,000 sites it monitors for customers, Chrome's share jumped to 4.4 per cent for the week of Dec. 6-12, an increase of 0.4 percentage points over Google's slice of the browser pie for the month of November.

Chrome's share during the week topped Safari's 4.37 per cent, said Vince Vizzaccaro, executive vice president of Net Applications. "It appears that Chrome has made a substantial surge in usage market share," Vizzaccaro said in an email.

Last week, Chrome accounted for 1.3 per cent of all browsers used on Apple's Mac OS X operating system, up from just 0.32 per cent during November. Chrome's gains came "fairly equally" from both Safari and Mozilla's Firefox, Vizzaccaro said. Like Chrome, Firefox is available in versions for Windows, Mac and Linux.

Chrome's post-beta jump was even larger on Linux, where Google's browser had a 6.34 per cent share of the open-source operating system's browser market for the week of 6-12 December, up from 3.81 per cent during November.

"I believe Linux will be the more intriguing arena to watch," Vizzaccaro said. "Firefox currently dominates browser usage on Linux the way that IE dominates Windows systems and Safari dominates Mac systems. With the emergence of Chrome, I'll be curious to see if Chrome will be to Firefox on Linux what Firefox is to IE on Windows ... a forceful competitor."

The availability of Chrome may also be the spark that finally pushes Linux's usage share above the 1 per cent mark, where it's hovered for years. During November, for instance, Linux had exactly 1 per cent of the OS share.

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Linux's high-water mark in the last two years was 1.17 per cent in May 2009. Vizzaccaro based his speculation of Chrome as a Linux driver not only on the browser itself, but also on the fact that it's the foundation of Chrome OS, the Linux-based operating system Google hopes to ship on netbooks by this time next year.

"Will Chrome on Linux and eventually on Chrome OS finally bring Linux usage beyond the 1 per cent range?" Vizzaccaro asked.

But for all of Chrome's gains, it remains far behind both Microsoft 's Internet Explorer (IE) - which runs only on Windows - and Firefox, the world's No. 1 and No. 2 browsers.

During November, IE had a 63.6 per cent share, while Firefox's was 24.7 per cent.