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The roles of Na, Mn, W and silica, and the synergistic effects between each metal in the Mn-Na2WO4/SiO2 catalyst have been investigated for oxidative coupling of methane (OCM). The crystallisation of amorphous silica during calcination at 900°C was promoted primarily by Na, but Mn and W also facilitated this process. The interaction between Na and Mn tended to increase the extent of conversion of Mn3O4 to Mn2O3. The formation of Na2WO4 was dependent on the order in which Na and W were introduced to the catalyst. The impregnation of W before Na resulted in the formation of Na2WO4, but this did not occur when the impregnation order was reversed. MnWO4 formed in all cases where Mn and W were introduced into the silica support, regardless of the impregnation order; however, the formation of MnWO4 was inhibited in the presence of Na. Of the prepared samples in which a single metal oxide was introduced to silica, only Mn/SiO2 showed OCM activity with significant oxygen conversion, thus demonstrating the important role that Mn plays in promoting oxygen transfer in the reaction. The impregnation order of W and Na is critical for catalyst performance. The active site, which involves a combination of Na-Si-W-O, can be formed in situ when distorted WO42- interacts with silica during the crystallisation process facilitated by Na. This can only occur if the impregnation of W occurs before Na addition, or if the two components are introduced simultaneously.