Sometimes referred to as cost-per- sale or CPS is an online advertisement pricing system where the publisher or website owner is paid on the basis of the number of sales that are directly generated by an advertisement. It is a variant of the CPA (cost per action) model, where the advertiser pays the publisher and/or website owner in proportion to the number of actions committed by the readers or visitors to the website.
In many cases, it is impractical to track all the sales generated by an advertisement. However, it is more easily tracked for full online transactions such as selling songs directly on the internet. Unique identifiers, which can be stored in cookies or included in the URL, are used to track the movement of the prospective buyer to ensure that all such sales are attributed to the advertisement in question.