A report by MediaPost claims that the highest-priced keyword in the US during September was $99.44 per click on Google. This data comes from the AdGooroo Search Engine Advertising Update, which has begun to track the click costs for search terms for the first time. According to their analysis, the term 'mesothelioma' was the highest-selling keyword, which was also sold on Yahoo! for $60.68 per click to get the top ranking position. The search term 'auto insurance comparison' was the highest-cost phrase on the Bing search engine, at $55.20 per click.

Of course, the search engines themselves will know this data but keep the information confidential, and it's not clear how the figures revealed by AdGooroo are obtained, other than by estimates and market feedback. It seems that the term 'mesothelioma' has become highly expensive due to legal firms pursuing new lawsuits related to the asbestos-causing lung cancer.

The report also says that the search engines served up on average between five and six ads per keyword during September. In the US market, Google moved to 5.45 adverts in September 2009, up from 3.06 a year before. Yahoo! dropped to 5.35 from 7.53 and Bing also saw a decrease to 3.10, from 5.12.