a method for easily and quickly determining the tendency of a petroleum fraction to foul in refinery equipment comprises determining the ratio of the saturates or aromatics : asphaltenes for the petroleum in question and comparing this ratio with a plot of ratios and fouling tendencies for a set of prior oils or resids . it has been found that the ratio and the relationship to fouling are completely consistent and reproducible phenomenon which thereby provide a rapid means for a substantially quantitative measure of fouling tendency .