Current ideas concerning oil rheology, in particular, that of heavy oils and water-oil emulsions have been considered. It has been shown that petroleum in general is a viscoplastic medium, whose rheological properties in many cases are satisfactorily described in terms of the simple Bingham model. Typical characterization of rheological properties reduces to measurement of the yield point and the pour point and to conditional values obtained by measuring viscosity in viscometers of various types. However, both the yield stress and plastic viscosity are structurally sensitive, resulting in dependence of the rheological properties of oil on the temperature and deformation history, including the kinetics of cooling, which is characterized by a hysteresis curve in the measurement of viscosity. The kinetics of change in the rheological properties of oil depends on the concentration of crystallizable paraffins and other components. Rheology is modified largely by introducing pour point depressants into the oil. Another method for controlling the rheological properties of oil is to convert it into the state of water-oil emulsion using various surfactants. The general formulation of the problem of pipeline oil transport has been discussed, involving calculation based on the knowledge of both the rheological properties of oil and the kinetics of transient structuring processes. The latter is especially important for start-up modes of pipeline operation.