We have made MINDO/3 calculations on a 47 silicon atom molecular cluster to model the diffusion of oxygen in silicon crystal. For interstitial oxygen (O1), we compute an activation energy for diffusion of 2.49 ev. We compute a binding energy of 0.1 ev. when two isolated interstitial oxygen atoms bond to a common silicon atom of the lattice. This complex (O2) is computed to move through the lattice with an activation energy of 1.36 ev. The diffusion path is through a four-member ring intermediate structure. We conclude that the diffusion constant for (O2) is eight orders of magnitude greater than that of (O1).