In this chapter we examine how hypertext based Internet applications support decision making in different purchasing situations. Our research methods are based on hyperknowledge framework, which is characterized to create an ideal computer based decision support system environment. We have performed three different purchasing case tests. In the two cases test subjects acquired a product or service from Internet without a defined www address or www page. In one case, test subjects used a definite product and www address. The test results of our study are based on comparisons between the above mentioned three cases. The comparisons suggest that if decision-makers use Internet based applications in complex purchasing situations, hypertext based Internet applications seem not to sufficiently support the purchaser’s decision making.