The interfacial behaviour of a crude oil and an asphaltene system has been studied by a planar rheological method. System S, was a 30% (v/v) xylene dilution of extra-heavy Cerro Negro crude oil; the aqueous phase was tridistilled water or an NaCl solution (2% (w/v)). System S2 was a 3.21% (w/v) dilution of Cerro Negro asphaltene in xylene; aqueous phase as for system S,. These systems were studied under creep in the pH range 1.6-9.5. The elasticity (E, and E,) and viscosity (ttr and qN) surface moduli were obtained from creep compliance measurements. Viscoelastic as well as elastic behaviour was observed. The interfacial rheological behaviour of asphaltene and crude oil systems was found to be very different in the presence and absence of salt. The high values of the moduli, leading to the high stability of water-in-oil emulsions, was attributed to flocculation of asphaltene-resin micelles at the interface. In the absence of resins, asphaltenes were not dispersed and their adsorption at the interface could lead to precipitation and multilayer formation.