The present paper deals with experimental and theoretical investigation of surface tension, apparent viscosity and viscoelastic properties of sal oil methyl ester biodiesel and its blends with petrodiesel at different temperature. Several methods were used to predict surface tension and apparent viscosity of biodiesel-petrodiesel blends. Satri-Rao method based on the corresponding state predicts surface tension of biodiesel-petrodiesel blends very well, whereas UNIFAC-VISCO group contribution method predicts apparent viscosity of blends very accurately. To predict the apparent viscosity of biodiesel, six unknown UNIFAC-VISCO group interaction parameters were determined and proposed parameters were then used to predict viscosities of biodiesel-petrodiesel blends. The recommendation was given which proportion of sal oil biodiesel and normal diesel was to be mixed to get the proper European standard grade diesel fuel. Viscoelastic properties (i.e., structural stability, storage modulus, loss modulus, complex viscosity and loss tangent) of biodiesel-petrodiesel blends were determined as a function of amplitude, frequency and temperature using parallel plates rotational viscometer in linear viscoelastic range. Finally, generalized Cox-Merz parameters were used to establish the relation between apparent viscosity and complex viscosity of blends. (C) 2015 Elsevier Ltd. All rights reserved.