A project was conducted from 1980 to 1982 to determine the costs and benefits of OCLC use in 29 small and medium-sized member libraries of the Illinois Valley Library System (IVLS). Academic, school, public, and special libraries participated by recording the time and staffing levels used for and the cost of OCLC and pre-OCLC cataloging (by in-house typing or duplicating of cards or purchase of vendor cards). It was found that (1) OCLC cataloging cost more than other methods, particularly for public and school libraries; (2) OCLC use provided a substantial reduction in staff cataloging time; (3) OCLC cataloging work was shifted to less expensive staff members in half of the libraries; (4) more cataloging information was provided when using OCLC; and (5) some libraries experienced decreased cataloging turnaround time with OCLC. Interviews with library directors and staff indicated other OCLC benefits, such as its use for interlibrary lending. A total of 22 of the 29 libraries decided to continue using OCLC after the project ended, despite its higher costs. This report describes project methodology and results with appendices presenting statistical information on project libraries, a map of IVLS, and sample worklog forms for the pre-OCLC cataloging studies and the OCLC cataloging study. (ESR)