The production of bitumen in Indian refineries is carried out by air blowing and component blending. In the component blending process, a highly viscous propane deasphalted (PDA) pitch is blended with a less viscous flux. The choice of the proportion of these two components is normally arrived at to meet the required technical specification such as penetration at 25°C and viscosity at 60 and 135°C. However, it is not clear at this point in time, the influence of constituent materials on the rheological response of the binder. In this investigation, two ratios of PDA pitch and Flux (75:25, 80:20) were blended in the laboratory. The rheological characterization of constituents and the final blend were carried out using a rotational viscometer at temperatures of 120, 140 and 160°C. Four viscosity mixing 'rules' were used to estimate the final blend viscosity from the individual constituent viscosities. The predictions varied with a wide range of errors. © ASCE.