"The initial subsurface sampling of oil in the West Basal Sundance reservoir, Lance Creek oil field, Wyo., was done by the Bureau of Mines in June 1937, about 2 years after discovery of the reservoir. The field was sampled to obtain data concerning saturation pressure, solution gas oil ratio, and shrinkage of a reservoir oil in a reservoir from which little oil had been produced. At this early date, meager data of this type were available for petroleum reservoirs. Unitization of the West Basal Sundance reservoir became effective January 1, 1938. The pressure maintenance program of injecting gasoline-plant residue gas into the reservoir was initiated February 23, 1938. Additional subsurface oil samples were obtained from selected wells in 1941, 1947, and 1948, primarily in an attempt to observe what effect the injected plant -residue gas might have on reservoir oil characteristics over a period of time. It was hoped that from the additional samples information might also be obtained regarding variation of reservoir-characteristics, as indicated by generally lower production gas-oil ratios of wells producing from structurally lower parts of the reservoir."