Liquid drilling fluid is often called drilling mud is heavy, viscous fluid mixtures use to carry rock cuttings to the surface and lubricate and cool the drill bit. During carrying cuttings they contaminated which not only reduce their functionality but also make them a hazardous and dangerous wastes which cannot be discharged anywhere without treatment. Due to this fact, in the present study, supercritical extraction process was used to remove contaminants from the drilling mud. Regarding this, effect of different parameters including extraction temperature (313-338 K) and pressure (100-200 bar), flow rate of CO2 (0.05-0.36 cm(3)/s) and static time (20-130 mm) on the removal of contaminations from drilling mud was examined using the design of experiment of changing one factor at a time. The obtained results revealed that the optimum operational conditions that lead to the highest removal degree of contaminations are temperature and pressure of 333 K and 180 bar, respectively, flow rate of lower than 0.1 cm(3)/s and the static time of 110 min. In addition, to examine the effect of the supercritical extraction on the crystalline structure modification and removal contaminations X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed which confirmed the successful removal of contaminations from the drilling mud without significant crystalline modification. (C) 2014 Elsevier B.V. All rights reserved.