Undergraduates use a wide range of information resources for academic and nonacademic purposes, including web sites that range from credible, peer reviewed, online journal sites, to biased and inaccurate promotional web sites. Students are taught basic critical appraisal skills, but do they apply these skills to make decisions about information in different web sites? In an experimental setting, undergraduate students examined pairs of web sites containing conflicting information based on different aspects of critical appraisal, namely credibility of the author of the information, purpose of the web site, and last update of the site, and answered multiple choice questions about the conflicting information. Results indicated that students failed to use critical appraisal criteria, and that while knowledge of and self-reported use of these criteria were related to each other, they were not related to behaviour. This research demonstrates the need for alternative strategies for critical appraisal instruction and assessment. (Contains 3 figures.)