The article is devoted to the conclusion of a semi-empirical dependence for calculating the volume coefficient of gas-saturated oils. For this calculation, the author of the article used expressions, which have been calculated earlier; the first expression is the expression of dependence for determining the volume coefficient at a gas saturation pressure of oils; the second expression is the expression for the compressibility factor of such oils. These dependences are based on a hypothetical model of the molecular structure of gas-saturated oils, developed on the basis of the J. I. Frenkel's hole theory of liquids. This fact, the physical validity of these expressions, and the basing of the obtained expression on a generally accepted dependence for determining the compressibility coefficient of a liquid under laboratory conditions give the final semi-empirical expression a theoretical character and ensure its applicability for a wide range of oils, which is confirmed by the verification of the expression, which is obtained in the article.