This paper presents a method of calculating the effects of the presence of non-absorbable gases on the performance of the absorber of vapour absorption refrigeration systems. The paper, which uses data for lithium bromide/water system with air as a contaminant, shows the detrimental effects of such gases on the overall effectiveness of the absorber. It is shown that the reduction in performance, due to the presence of a non-absorbable gas, can be offset by either introducing turbulence into the vapour/gas mixture in the absorber or choosing a larger absorber. Calculations of the reduction in COP, due to hydrogen build-up in the absorber of a LiBr/ H2O system, are also presented.