Bing's share of U.S. search queries rose slightly from 9.3 percent in August to 9.4 percent last month, while Google, out alone in first place, increased its share from 64.6 percent to 64.9 percent, comScore on Wednesday.

Yahoo took a small tumble, as its share of queries fell by half of a percentage point to 18.8 percent, leaving it in a distant second place.

Overall, U.S. Internet users ran 13.8 billion searches in September, 1 percent less than in August.

Since Bing's introduction in late May, search industry experts have been watching intently to see how much headway Microsoft makes in a market where it hasn't enjoyed as much success as it has hoped to.

Bing has certainly improved Microsoft's market share, which stood at 8.4 percent in June, but not in a radical fashion, especially considering that Microsoft is reportedly spending about US$100 million to promote the search engine.