Google Inc.'s audience is growing so fast the Internet search giant's collection of Web sites are likely to supplant rival Yahoo as the world's most popular in about a year, Citigroup analyst Mark Mahaney wrote in a note to investors.

Mahaney based his conclusion on figures for September Web traffic provided by comScore Networks.

By climbing the rankings, Google is sure to see a gain in revenue-producing potential. That's because the Mountain View, Calif.-based firm generates nearly all its revenue when someone clicks on an advertisement alongside its Internet search results, or other Web sites. The larger the audience, the theory goes, the higher the likelihood someone will click on a Google-placed ad.

Yahoo Inc. now operates the top Web site, with 130 million unique visitors in September, according to the comScore data; No. 2 is Time Warner Inc., with 120 million unique visitors and No. 3 is MSN-Microsoft, with 118 million.

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