The effect of additives on the viscosity of liquid-phase dimethylaluminum hydride (DMAH) was investigated. The viscosity of pure liquid-phase DMAH was measured to be 6400 cp (centipoise) but the viscosity of liquid-phase DMAH was drastically reduced down to 50 cp with the addition of 2.7 mol% diethylphenylphosphine, 60 cp with 0.4 mol% tribenzylphosphine, 70 cp with 2.4 mol% trihexylamine, and 30 cp with 1.4 mol% 3-benzylpyridine. The electron donating ability and steric effect of the additives are believed to be the most important factors in lowering the viscosity of DMAH. By reducing the viscosity of liquid-phase DMAH, the bubbling efficiency was significantly improved. State of gas-phase DMAH was also monitored by in situ Fourier transform infrared spectroscopy (FTIR). In the gas phase, trimeric form and hydrogen-bridged dimeric form of DMAH were observed up to 170 degrees C and between 170 degrees C and 250 degrees C only hydrogen-bridged dimer was observed. Above 250 degrees C, methyl-bridged dimer appeared and above 320 degrees C methane and aluminum was observed from the dissociation of DMAH.