Correlation - "OPEC increased oil price and OPEC import costs" by the Petroleum Industry Research Foundation, Inc., August 27, 1975, Box: 17, Folder: 4. Charles Heller papers, RH MS 314. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/490348 Accessed April 25, 2024.