Abstract Instantaneous producing gas-oil ratio histories are calculated for a large number of hypothetical solution-gas-drive reservoirs from the basic data used by Arps and Roberts, and the results are presented in graphical form. A correlation is thus established wherein a typical GOR history can be obtained for a given gravity oil, with a given solution GOR, produced from a given type of reservoir rock. Introduction In 1955, Arps and Roberts presented the results of 72 solution-gas-drive recovery computations made on hypothetical reservoirs. The study covered six different types of reservoir rocks representing maximum, average and minimum conditions for sandstones and limestones. These six types of reservoir rock were assumed to be saturated with 12 synthetic crude-oil and gas mixtures representing oil gravities of 15 degrees, 30 degrees and 50 degrees API, and solution gas-oil ratios of 60, 200, 600, 1,000 and 2,000 scf/STB. The calculations, made using a Muskat-type differential equation, resulted in the relationship of stock-tank oil recovery (as a fraction of total pore volume) vs reservoir pressure for each hypothetical reservoir. From these data a correlation was developed between oil recovery and original solution GOR, API oil gravity and type of reservoir rock. The purpose of the present paper is to extend the original work of Arps and Roberts by presenting calculations of the instantaneous producing GOR histories for these same hypothetical sandstone reservoirs. The solutions representing the limestone cases have been omitted. Gas-Oil Ratio Equation The instantaneous producing gas-oil ratio R can be calculated by the following equation. . . (1) JPT P. 595^