We present a transport model for asphaltene diffusion from an oil/water interface through a water film followed by adsorption at a solid/water interface. Using a Langmuir adsorption isotherm, the effect of asphaltene aqueous solubility and adsorption constant K on equilibration time are established. For K greater than 1 nm and asphaltene solubilities down to 0.1 ppb, adsorption equilibrium, taken to be 1 mg/m{sup 2}, occurs within a few hours. Negligible asphaltene solubility does not explain why a water film prevents asphaltene adsorption and wettability alteration in reservoir rock.