The effects of high temperature pretreatments on the activity of MgO and Li/MgO catalysts for the oxidative coupling of methane have been studied. The MgO powder catalyst exhibited a turnover frequency of 3.0 x 10(-3) molecules/site s, at 990 K, whereas the Li/MgO catalyst showed a turnover frequency of 7.0 x 10(-2) molecules/site s, under the same reaction conditions. The initial C-2 formation rate was observed to increase with pretreatment temperature over the MgO catalyst, supporting our previous proposal that F-type defects are responsible for methane activation.