A study of the effect of the ball-milling gas environment on the kinetic enhancement of MgH2 with different additives was conducted using argon and hydrogen. The as-sourced MgH2 was milled for 20 h and then milled for a further 2 h after adding 1-2 mol% of one of the additives titanium isopropoxide, niobium oxide or carbon buckyballs, varying the gas environment for both ball-milling stages. The milling environment had little or no effect on the desorption kinetics in most cases. However, in some cases, the absorption uptake differed by up to 2 wt%, depending on the gas used. This effect was not consistent among the composite samples surveyed, demonstrating the importance of reporting all information about the ball-milling processes used, including the gas environment. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.