Bitumen, a very heavy crude oil, contains both water-soluble and water-insoluble natural surface active species. This study shows that complete removal of the water-soluble surface active species from bitumen by water extraction resulted in an increased emulsion stability and that the water-insoluble surface active asphaltenes are the key stabilizing agents for water-in-toluene-diluted bitumen emulsions. Separation of the toluene-diluted bitumen continuous phase from the emulsion by centrifuging at 1, 10, 100, 1000 and 10,000g was conducted. Emulsion stability tests fur the separated toluene-diluted bitumen and element analysis of the precipitated asphaltenes indicated that the asphaltenes in the separated organic continuous phase are different from those associated with the water droplet interface. The asphaltenes associated with the interface had a lower H/C ratio and a higher O/C ratio. (C) 2002 Elsevier Science Ltd. All rights reserved.