The necessity of development of new methods of express control of hydrocarbon media and their mixtures, especially volatile ones is proved. The problems arising when controlling the condition of volatile hydrocarbon media using the phenomenon of refraction are noted. A new method for determining the components and the ratio between their concentrations in a mixture of volatile hydrocarbon media has been developed. The use of the new method makes it possible to determine the composition and percentage content of the components in hydrocarbon mixtures. The design of a small-size refractometer for the implementation of the new method has been developed. There are no analogs of the new method and refractometer design. The developed instrument can also measure n with an error of ±0.0004 in the range from 1.250 to 1.740. This is sufficient for express control of the state of all hydrocarbon media and their mixtures. The results of studies of gasoline and oil mixtures are presented.