It is not uncommon to see a Google AdSense ad with either one big ad from a single advertiser or many ads from multiple advertisers. But why would Google decide to ever show only one ad, as opposed to many?
That was the topic of a Google Groups thread where Google AdSense representative, Ashley, responded with the answer.
She said that these single ads are called "expanded text ads" and can be displayed in either a placement-targeted or a keyword-targeted text ad. Now, placement-targeted text ads always expand to fill the entire ad unit. However, keyword-targeted text ads may or may not show a single ad - it depends on if Google determines that "a larger ad will perform better for a particular page," said Ashley.
This post was pre-written and scheduled to be automatically posted today.