1. Berl , Ernest , “ Art of Extracting Oil from the Earth ,” U.S. Patent 2 , 267 548 ( 1941 ).
2. Cooper , J.E. “ Oil Recovery Method Employing Acids -Extracted from Crudes Using an Ion-xchange Process ,” U.S. Patent 4 , 037 656 ( 1977 ).
3. Csaszar , Albert K. “ Solvent-Waterflood Oil Recovery Process ,” U.S. Patent 3 , 163 214 ( 1964 ).