Three candidate asphaltene inhibitors have been laboratory tested for their effectiveness on a Canadian crude. One inhibitor, an oil-soluble polymeric dispersant developed by Shell Chemicals, showed superior behavior compared with the others; flocculation titrations with n-heptane resulted in an optimum concentration of 1300 ppm. PVT calculations, however, indicated that the prevailing conditions downhole can be quite favorable with respect to the amount of effective inhibitor compared with the atmospheric laboratory titrations, which appear to be quite severe tests. Therefore, lower initial concentrations were recommended for a field trial. The chemical could be injected continuously through a capillary string, thereby avoiding the lost oil production associated with solvent-cleaning operations. It has proved to be very effective at concentrations as low as 66 ppm, resulting in both a technically and economically successful trial.