Dissipative particle dynamics simulations of a meso.scale model are performed to investigate the concentration dependence of surfactant adsorption on small-diatrieter carbon nanotubes and their bundles. Adsorption is found to follow fundarnentally different mechanisms in the two cases because of the heterogeneity of the bundle surface and the difference in diameter of bundlescorn pared to that of individual tubes. Whereas aggregation dominates adsorption on individual tubes, oil bundles it is largely a Latigntuir-type process. High adsorption energy sites on the outer surface of bundles, where surfactant molecules can interact with two tubes simultaneously, dominate at low coverage. They also cause adsorption oil bundles to become significant well before adsorption on individual tubes starts. The difference in the adsorption mechanisms leads to a crossover point at higher concentrations, where the adsorbed amount per surface area oil individual tubes becomes larger than (hat for the bundles.