Special pseudo-components (SPCs) are proposed to be the compositional entities for characterizing the complicated mixtures of stock and product oils involved in fluid catalytic cracking risers. SPCs have invariant and definite physicochemical properties and are defined in pairs of light and heavy oil cuts of narrow boiling range. A narrow cut of true boiling point distillation of a stock or product oil is expressed with a pair of SPCs, which constitutes the basis for the characterization procedure developed in this paper. A steady state model for a prototype riser with a side feed stream is formulated where material and heat balance is strictly observed, the hydraulic behavior is considered, and the kinetic scheme of Gupta et al. (2007) is adopted. Results of tests with production data from three commercial risers show that the kinetic scheme of Gupta it al. (2007) is predictive as coupled with the suggested characterization procedure in the sense that for a given riser and given catalyst, the kinetic parameters are independent of stock oils. (C) 2013 Elsevier Ltd. All rights reserved,