A statistical mechanical model of gas solubility in glass is presented. For equilibrium, the Gibbs free energy of the free gas is equated to that of the gas in solution. Expressions for the Gibbs energies are obtained from assumptions of the atomic motion in the free gas and dissolved states. The resulting solubility equations express the solubility (in atoms per cubic centimeter of glass) as a function of gas pressure, temperature, fundamental constants, and material parameters. An initial evaluation of the model is made by comparison with literature data for helium and neon in fused silica.