Imperial Gas Tanks Imperial Gas Tanks Year Description Quanta # 1967 - 73 Gas Tank, w/o Vent CR-20A 1967 - 73 Gas Tank, w/ 2 Vents CR-20B 1967 - 73 Gas Tank, w/ 4 Vents CR-20C 1974 - 75 Gas Tank CR-22A 1990 Gas Tank CR-7A 1991 - 93 Gas Tank CR-7B