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 in the project. Based on written attitude surveys of and interviews with library directors, staff, patrons, and members of the library governing board or other governing authority, this publication describes: (1) expectations of OCLC and the project; (2) attitudes toward specific facets of OCLC, covering attitudes toward cataloging and resource sharing on OCLC, staff effectiveness/satisfaction with OCLC, public relations and OCLC, clustering and public access terminals, and OCLC costs and other disadvantages; (3) the medium-sized public library that did not continue OCLC use; (4) attitudes toward the project and post-project needs; (5) the differences between attitudes of library directors and governing authorities; and (6) factors influencing the decision to continue or discontinue OCLC use after the project ended. Extensive appendices present statistical information on project libraries; a map of IVLS; sample questionnaires; full details of the responses to all attitude surveys and interviews; and a sample OCLC decision packet outlining OCLC benefits, disadvantages, and costs in a format designed to help library directors make a decision on further OCLC use. (ESR)