Rheological properties of Buchan crude oil—water interfaces have been determined using a biconical bob rheometer. The effects of temperature and the presence of surface-active demulsifiers on film characteristics have been evaluated. Free oscillation and creep modes have been used, depending on the relative viscoelastic behaviour of the films. Film ageing is particularly significant, whilst temperature and the nature and concentration of any demulsification chemicals also contribute significantly. Further detailed understanding of interfacial film rheology is considered to be desirable for a complete appreciation of the stability of water-in-crude oil emulsions.