Surfactant formulations that are used in enhanced oil recovery consist of mixtures of various components. We have continued studies on mixtures of an anionic surfactant, C/sub 8/benzenesulfonate, and a nonionic surfactantt. C/sub 12/EO/sub 8/alcohol. Adsorption data on alumina and silica show that strong interactions between the two surfactants occur. On alumina on which the nonionic does not absorb by itself the presence of small amounts of adsorbed sulfonate was sufficient to cause significant adsorption of ethoxylated alcohol. On silica sulfonate did not absorb by itself but only did so in the presence of alcohol. Interactions between surfactants were quantified using the regular mixing model. Interaction parameters between -3 and -5 were determined at the liquidair interface in mixed micelles from surface tension data for different surfactant compositions. Work is focused on directly measuring thermodynamic quantities using microcalorimetry. Surfactant structural effects were also studied. A series of branched C/sub 14/benezenesulfonates emphasizes characterization along with adsorption measurements. Results showed major influences in addition to that of chain lenth and chain branching due to the position in the benzene ring of the longer alkyl chain in relation to that of the sulfonate group. 43 refs., 54 figs., 3 tabs