Four competing unimolecular decomposition pathways for disilane are considered with use of MP4 energies obtained with an extended basis set and geometries obtained at the MP2/6-31G** computational level. The 1,1- and 1,2-eliminations of H2 and the elimination of silylene to form silane all have similar endothermicities, but the very high activation energy for the I ,2-elimination eliminates this process as a significant contributor at low energies. If disilene is formed in the thermal decomposition of disilane, the more likely source is its higher energy isomer silylsilylene via a relatively low energy I ,2-hydrogen shift.