The surface and thermodynamic properties of some synthetic surfactants, as well as their efficiency as collectors in the flotation of petroleum coke, are studied. These surfactants are monoisomeric alkylbenzenesulfonate of different alkyl chains (C12 to C14). The results show that the length of the hydrocarbon chain of these surfactants plays a major role in determining their surface and thermodynamic properties. The values of surface excess concentration (Gamma(max)) and Gibbs energy of micellization (Delta G(mic)(o)) are found to increase with increasing number of carbon atoms in the chain while the values of critical micelle concentration (cmc) are decreased. The results indicate, also, that there is a good relationship between effectiveness of adsorption of a surfactant and its efficiency as a collector. A surfactant of higher Gamma(max) produces a concentrate of lower ash content and higher flotation yield. Thus, the surfactant with longer alkyl chain (C14) and highest Gamma(max) value is more selective, as a collector, than others of shorter carbon chain.