Using Ehrenberg's application of mathematical models to the analysis and prediction of repeated buying patterns of consumers, this study focuses on the concept of library use as a form of consumer behavior. The following hypotheses were tested: designated library user groups will tend to exhibit stable behavioral patterns with respect to the library; these behavioral patterns will be found to be similar to those identified with respect to the consumption of frequently bought products; and the NBD (negative binomial distribution) model can be used as a reliable predictor of the repeat use behavioral patterns of library users. In a comparative study, the borrowing activity of faculty, postgraduate students, and university support staff at Cranfield Institute of Technology (England) and the University of Waterloo (Ontario, Canada) was analyzed through the collection and analysis of library transaction data over a 4-week period. Findings indicated that: (1) In both long- and short-term studies at Cranfield and Waterloo, clearly defined and consistent patterns of behavior emerged. These patterns relate not only to the degree to which each segment of the user community borrows material, but also to the types of material that the users affiliated with a particular department or discipline tend to use; (2) There are significant similarities between the behavior of library borrowers and behavior identified in numerous consumer research studies of repeated buying; and (3) The NBD repeat buying model provides a close fit between its theoretical predictions and the observed behavior of library borrowers. Eleven figures and 46 tables illustrate the study. (Contains 66 references.) (MAS)