As a means of making available and acquiring e-books, Stockholm University Library uses PDA and EBS models. In order to improve the knowledge of the benefits and drawbacks of these purchasing models, the library has undertaken a major evaluation of ten agreements with various publishers and aggregators. This session will, among other things, address the following questions: What is the average price per book at the time of purchase? What is the cost per use? Do purchased titles continue to be used? What is the usage by subject area and by year of publication?