In oil/water/solid contact angle experiments, aluminum alloy surfaces with a high percentage of MgO in the oxide layer were wetted by naphthenic oil and naphthenic oil containing 1 percent oleic acid. The opposite behavior, poor wetting, was observed on alloy surfaces of almost pure aluminum oxide. On the latter surfaces, however, oil wetting was increased by decreasing the pH and by adding magnesium ions to the water being displaced.