One of the treatment techniques used for oil separation from oily wastewaters is membrane filtration. Dimensional analysis of steady state and unsteady state permeation flux was studied for microfiltration (MF) of synthetic oily wastewaters using mullite ceramic membranes. Mullite membranes were synthesized from kaolin clay as MF ceramic membranes. In order to determine the optimum operating conditions, 250-3000 ppm condensate gas in water emulsions were employed as synthetic oily wastewater. In steady state condition, three dimensionless numbers were definded as shear stress, resistance and Reynolds numbers. The shear stress number (N-S) compares shear stress at the membrane surface with pressure, while the resistance number (N-f) compares convective crossflow transport with derived transport through a layer, whose resistance is sum of all the resistances induced by different processes which limit mass transport. In unsteady state condition, two dimensionless numbers were definded as flux and time factors. Experimental data obtained in MF of the oily wastewaters were recalculated in terms of these dimensionless numbers for steady state and unsteady state conditions. At steady state condition Ns increases as cross flow velocity increases but Nf increases at low cross flow velocities and decreases at high cross flow velocities. Dimensional analysis of unsteady state condition showed that increasing oil content enhances membrane fouling rapidly and this decreases flux factor. Also, increasing cross flow velocity and temperature increases flux factor and decreases membrane fouling. (C) 2009 Elsevier B.V. All rights reserved.