First principles calculations using density functional theory (DFT) are reported for two layers of methane adsorbed on the (100) surface of MgO. The lowest energy structure determined has a first layer with C2v methanes adsorbed above magnesium atoms, with hydrogen atoms pointed towards neighboring oxygen atoms, and a rotation of 90° in between each neighboring methane. The second layer methane layer has a similar structure, except the hydrogen atoms are directed towards nearest neighbor magnesium atoms. It is found that the structure of the first layer has a large effect on the relative energies of proposed bilayer structures, as does the calculated separation between the two layers of methane. Competing roles of surface-adsorbate and adsorbate-adsorbate interactions are also discussed.