The thermal properties and characteristics of the molecular structure of petroleum and bitumen emulsions were investigated by viscometer and Rayleigh light scattering. The viscosity, structural properties, and character of the intermolecular interactions in the emulsions are determined by the temperature of formation of these media. Formation at "critical" temperatures close to 36-38degreesC initiates a structural phase transition that alters the size and activity of molecular aggregates of asphaltenes. These aggregates serve as binder material in three-dimensional supramolecular structures containing wax microcrystals. The long (up to several months) "memory" of the emulsions concerning the conditions of formation is due to the strength of the three-dimensional structures that contain not only hydrogen but also covalent bonds.