Bing, Microsoft's new search engine, is making steady if unspectacular progress in its bid to wrest a bigger share of the lucrative US search and advertising market away from Google.

Bing increased its share of the US search market to 9.4 percent in September from 9.3 percent in August, according to figures released Wednesday by online tracking firm comScore.

It was the fourth month in a row of modest gains for Bing, which the Redmond, Washington-based software giant unveiled in late May accompanied by a 100-million-dollar advertising campaign.

Google, meanwhile, increased its share of the US search market to 64.9 percent in September from 64.6 percent in August, comScore said.

Yahoo! saw its market share fall half-a-point to 18.8 percent in September. Ask.com and AOL were unchanged at 3.9 percent and 3.0 percent respectively.

Yahoo! and Microsoft, after months of negotiations, unveiled a 10-year Web search and advertising partnership in late July that set the stage for a joint offensive against Google.

Under the agreement, Yahoo! will use Microsoft's search engine on its own sites while Yahoo! will provide the exclusive global sales force for premium advertisers.

The agreement between the Internet portal and software giant, which is subject to review by US anti-trust regulators, is expected to close in early 2010.