The adsorption kinetics of asphaltenes at the toluene - silica interface has been measured for nine solution concentrations CS (from 5 to 3000 mgL-1) Results could be adjusted to an irreversible second-order adsorption kinetics, where the adsorption rate k was strongly dependent on concentration. Thus a large reduction in k was observed when CS was increased in the studied concentration range. This rate reduction was accounted for in terms of adsorption of aggregates formed in solution. The step - wise trends observed for the adsorption isotherms of asphaltenes on mineral surfaces, could be reproduced using the above k values.