Even though asphaltenes do not have the well-defined amphiphilic structure characteristic of surfactants, it has been shown that they can stabilise water-in-oil emulsions. We propose that this stabilisation occurs because asphaltene aggregation results in the formation of a network within the thin oil film separating approaching emulsified water droplets. This network changes the rheology of the film to non-Newtonian, which prevents drainage of the film at thicknesses less than about 50-100nm. The presence of the network also imparts steric stabilisation to the emulsion. The proposed stabilisation mechanism does not invoke any surfactant-like behaviour of asphaltenes. Instead, it relies solely on their propensity to aggregate.