This interlibrary loan (ILL) cost study was conducted at Union College Library in Schenectady, New York, in order to provide immediate feedback about ILL as well as to serve as a potential management tool for library and college administrators. This report describes the financial statistics of a 3-year period of use of ILL services at this small, private college library. Following a review of previous cost studies, the researchers chose to use available year-long data sets to calculate (rather than estimate) interlibrary loan transaction costs as precisely as possible. Costs per transaction were calculated based on the actual costs of insurance, fees, and charges incurred by the library on behalf of patrons; telecommunications; local library council dues; salaries, wages, and fringe benefits; and on closely figured estimates of postage, photocopying expenses, and overhead for all regular and student employees' salaries and wages. This paper includes an interpretation of the study results, discussion and conclusions, and numerous tables presenting the detailed costs by academic year and percentage increases in both extra-organizational ILL cost components, and extra-organizational cost shifts. (THC)