The proper understanding of rheological characteristics of CGA based fluids is of crucial importance in determining the performance of the fluid, in order to maintain the most effective fluid properties for safe, efficient, and economical drilling operation. This paper presents a concise investigation on the effect of concentration of the three main components of a novel environmentally friendly lightweight CGA based drilling fluid, i.e., xanthan gum biopolymer, starch, and biosurfactant, to the Herschel-Bulkley rheological model parameters. The three parameters of Herschel-Bulkley model, i.e., yield stress, fluid consistency, and fluid flow index were calculated by fitting the experimental data of shear stress as a function of rate of shear to the model. Results of data fitting analysis show that Herschel-Bulkley model performs satisfactorily well in describing the rheological behavior of CGA based fluids with R-2 greater than 0.99. Moreover, experimental results indicate that the increment of the amount of three main components increase the yield stress of the final CGA based fluid as the flow resistance is increased. Furthermore, the result also showed that the calculated fluid consistency of the drilling fluid appears to be strongly dependent on the presence of xanthan gum and starch. However, the fluid consistency appears not to be affected by the presence of salt. It is also concluded that the formulated CGA based fluids have shear-thinning behaviors with values of fluid flow indices (n) 0.2-0.3. The results of this study can be helpful in determining the appropriate procedure for utilizing the CGA based fluids in oilfield operations. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.