Ads can come from your competitors or ads might come from the same company selling the ad space. Regardless, all ads are competing for the same audience attention and your ad must be able to capture the audience's interest from all the other advertisements. Many web sites offer multiple slots where banner space can be purchased: top (generally the most expensive), down the left or right side, and bottom. If a banner ad is not placed on the top part of the screen, it is less likely to be noticed.