Surfactants can be used to alter wettability of reservoir rock, increasing spontaneous imbibition and thus improving oil yields. Commercial synthetic surfactants are often prohibitively expensive and so a crude preparation of the anionic biosurfactant, surfactin, from Bacillus subtilis, able to be grown on high-starch industrial and agricultural effluents, has been proposed as an economical alternative. To assess the effectiveness of the surfactin, it is compared to a commercially available surfactant. We review the literature to survey the adsorption models that have been developed to describe surfactant adsorption in porous media. These models are evaluated using the experimental data from this study. Crushed carbonate rock samples were cleaned and aged in crude oil. The wettability change mediated by dilute solutions of commercial anionic surfactants and surfactin was assessed using a two-phase separation, and surfactant loss due to retention and adsorption on the rock was determined.