Solid-stabilized water-in-oil emulsions cause many problems such as oil loss, fouling of a processing unit, and environmental hazard in the petroleum production and refining. The ability of finely divided solids to stabilize these emulsions is due to the adsorption of asphaltenes and other heavy constituents. This study presents the individual and competitive adsorption of asphaltene functionalities in cyclohexane solution and asphaltene in heptol solution onto goethite (FeOOH) particle surfaces at 25 degrees C to quantitatively understand the FeOOH particle-fluid interactions. The functionalities used were carboxylic acid (represented by benzoic acid), sulfoxide (by diphenylsulfoxide), and pyrrolic (by indole). The single component adsorption of these functionalities was well represented by both the Langmuir and Freundlich models, showing that adsorptive affinity for FeOOH increased in the order of indole < diphenylsulfoxide < benzoic acid. This observation was supported by the results of bi-component competitive adsorption of three functionality pairs on FeOOH, which were interpreted by the Fritz model. The adsorption of asphaltene was performed using dry and moist FeOOH surfaces and well represented by both the Langmuir and Freundlich models. The moist FeOOH yielded a decrease in the adsorption of asphaltene compared to adsorption on dry FeOOH.