The PTC model shares some similarities with pay to surf as both of these models use referral marketing as a promotional method. Bitsurf looks to be one of the most profitable paid-to-click sites, if it can get up and running. PPC «display» advertisements, also known as «banner» ads, are shown on web sites with related content that have agreed to show ads and are typically not pay-per-click advertising. In contrast, content sites commonly charge a fixed price per click rather than use a bidding system. Purpose Pay-per-click, along with cost per impression and, are used to assess the cost effectiveness and profitability of internet marketing. The marketers can encourage the referring parties by providing pre-scripted messages.