Research on the adsorption phenomena present during fluidized catalytic cracking of hydrocarbons was carried out utilizing a novel unit developed at CREC-UWO : the Riser Simulator reactor. A series of cracking experiments were carried out using commercial gas oils and cracking catalysts which resembled the ones used in industrial FCC units. Determination of the adsorption coefficients of the various hydrocarbon lumps was possible using mass lump balances and total pressure changes. Given experimental results and subsequent numerical analysis, it was found that the adsorption coefficients were mainly related to molecular weight and reaction temperature with the influence other factors being less relevant.