Rheological investigation and correlation development for the flow of heavy oil (HO) were done in a temperature range of 30-50 degrees C in the presence of natural surfactant extracted from Madhuca longifolia (ML) and potato starch (PS) along with water cut (0-15 vol/vol %). Viscosity of HO reduced by 41.7% after 1000 ppm ML addition at 50 degrees C. Viscosity reduced by 35.3 and 25.9% after addition of 2000 ppm of ML and PS, respectively, at 30 degrees C and 600 s(-1) to the 95% HO + 5% water. Similarly, maximum viscosity reduced to 45.1 and 34.7% with 15% water cut at 30 degrees C and 600 s(-1) after addition of 2000 ppm ML and PS, respectively. The HO was found to follow power law rheological model before and after addition of water, ML, and potato starch at each temperature. A new heavy oil viscosity correlation was developed considering the individual and combinational impacts of temperature, shear rate, water cut, and concentration of ML and PS using response surface methodology. Correlation with combinational factors showed greater accuracy in determining HO viscosity. Thus, natural extract ML and PS can be used as alternative to heating, and the new correlation using the combinational factors of temperature, shear rate, water cut, and concentration of ML and PS may be useful to predict HO viscosity with greater accuracy.