An investigation of the interlibrary loan (ILL) borrowing patterns of six academic libraries and one large urban library--all members of the Colorado Alliance of Research Libraries (CARL)--analyzed data on transactions carried out through the OCLC ILL system during the 3 month period of March through May of 1988. The data and analyses focused on the: (1) number and type of lending institution; (2) number of loans by state; (3) types of libraries from which loans were made; (4) number of items borrowed per CARL library; (5) number of titles borrowed by Library of Congress classification letter; and (6) number of items by year of publication of item. One study result showed that CARL members overwhelmingly borrow from within the state of Colorado whenever possible; when it is not, they tend to borrow from libraries in the southwest and midwest United States; and twice as many items are borrowed in the humanities and social sciences as in the physical and natural sciences. It is noted that OCLC data provide a valuable way to analyze interlibrary-loan traffic. Concluding the report are the following appendices: (1) Interlibrary Loan Policy, Arthur Lakes Library, Colorado School of Mines; (2) Rules for the Administration of the Colorado Library Network--Payment for Lending Program; (3) BCR Interlibrary Loan Code; and (4) a report from the CARL User's Group ILL Task Force. (26 references) (Author/MAB)