The statistical design of experiments (DoE) was used in the process study of oxidative coupling of methane (OCM) over Na-W-Mn/SiO2 catalyst. A set of factors with a certain range was screened using factorial design with respect to three responses: methane conversion, C2+ products selectivity and ethylene/ethane ratio. The variances were analyzed and the interaction effects of the process parameters were evaluated. With the understanding of the process, the optimization of the process was further studied using response surface methodology coupled with central composite design (CCD). The optimum conditions were obtained as reaction temperature = 850 degrees C, gas hourly space velocity = 23 947 cm(3) g(-1) h(-1), catalyst pretreatment period = 2 h, dilution ratio = 0.2 and CH4/O-2 ratio = 7.40.55% of methane conversion and 79.51% of C2+ product selectivity were obtained under these optimum conditions. Experimental runs under optimum conditions were repeated and compared with the simulated values obtained from the model. There was good agreement between the experimental and simulated values. (c) 2007 Society of Chemical Industry