Rapid alkyl exchange reactions in gas phase mixture of trimethylamine alane and trialkylgallane lead to a statisticall mixture of trialkylgallane. Partial pyrolysis of these mixtures leads to selective /3-elimination of ethyl groups, resulting in a mixture of dialkyl and monoalkylgallanes, which have been characterised by FI1R, proton NMR and mass spectrometry. The mass spectrometric observations revel the presence of dimeric and trimeric species. The NMR results confirm this conclusion, and further suggest that interamolecular exchange processes are fast even at 200 K, whereas intermolecular exchange is significant only above 250 K.