The colloidal stability index (Heithaus parameter) was detd. for 2 types of crude oil differing in phys.-chem. properties and for their mixts. (25, 50 and 75% by mass) by turbidimetry. The relationship between the Heithaus parameter and content of particular hydrocarbon groups was plotted and the optimal mixt. compn. was detd. The result of prediction by using the developed model were confirmed by a modified hot filtration test.