The coking ability of some hydrocarbons (benzene, n-heptane, styrene, methy
lnaphthalene, durene, and phenanthrene) and heterocyclic compounds (thiophe
ne and indole) under the conditions of hydrotreatment of feed is estimated
for an Ai-Co-Mo catalyst. The method of isotopic labels is used to determin
e the contributions of the components of binary mixtures to the formation o
f coke on the catalyst surface. These contributions do not coincide with th
e values of coking ability found for individual compounds.