Watkins, J. W.; Willett, F. R. & Arthur, Charles E. Conditioning Water for Secondary-Recovery in Midcontinent Oil Fields, report, December 1952; (https://digital.library.unt.edu/ark:/67531/metadc38591/m1/1/: accessed August 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .