The expediency of using calculation methods to predict the yield and properties of catalytic cracking products upon variation of the feedstock quality for further extending oil processing was shown. The catalytic cracking of mixed types of feedstock, such as a mixture of vacuum distillate with sulfurous atmospheric residue or low-sulfur paraffin vacuum residue, was studied at a pilot plant. Computational equations were derived to describe the dependence of the amount of aromatic hydrocarbons in light and heavy gas oils and of the correlation index of heavy gas oil on the quality of the mixed feed and cracking conditions.