The amount of traffic provided to each advertiser depends on how prominently their adverts are shown. The sponsored results shown above the organic listings tend to have much higher amounts of traffic, making them the preferred advert location. Although not strictly proportional, the higher the adverts position on the page, the more people tend to click on the advert. As such, Adwords ranks the adverts with the most desirable at the top of the page, and the less desirable being near the bottom or not even on the first page of results.

The ranking of adverts is based on many factors with the most important being bid price and quality index where the quality index is made up of factors like the advert click through rate (CTR). There is a great skill in being able to reduce bid prices whilst ranking highly by boosting the quality score for an advert.

Google Adwords is not the only pay per click service, but it is by far the biggest with current estimates putting its market share at 85%-90%. The biggest competitors in the UK are Yahoo Search Marketing (the new name for Goto.com who were bought out by Overture) and Microsoft Adcenter.