Adsorption of surface-active components from Athabasca bitumen at an oil-water interface was studied using a Langmuir interfacial trough. Langmuir films of bitumen, maltene, and asphaltene were prepared at a toluene/water interface. These films were subjected to multiple washings with toluene. Asphaltenes were found to be irreversibly adsorbed at the toluene/water interface because no noticeable change in interfacial pressure-area (pi-A) isotherms was observed when asphaltene films were repeatedly washed with toluene. In the case of bitumen films, the pressure-area (pi-A) isotherms showed a consistent shift upon the first two consecutive washings. No further shift was observed when the bitumen film was further washed. Isotherms recorded after the two washings of bitumen films were identical to that of the original asphaltene films. Pressure-area (pi-A) isotherms would indicate that the bitumen film present at the toluene/water interface was mainly composed of asphaltenes.