Previous work found the gas hold-up in a tall, 0.15 m(3) vessel, agitated by three impellers, to decrease considerably with temperature. This was attributed to a decrease in liquid viscosity, a decrease in surface tension or a decrease in gas density. The aim of this work was to investigate the influence of gas density on the gas hold-up. First of all, it was attempted to reproduce the data found in literature. It was shown that contaminants had a significant impact on the gas hold-up. Experiments with increasing and decreasing amounts of tap water (as the source of the contamination) found the gas hold-up to be affected by a strongly absorbing non-ionic surface active agent. Experiments in a system exhibiting low conductivity and low gas hold-up showed that the gas hold-up decreased by 15% for temperatures between 295 and 350K. Experiments with helium as sparging gas found that gas density does have a lowering effect on the gas hold-up. The gas hold-up did not change for temperatures above 350K, which may be due to the increased presence of micro-bubbles in a near-boiling system.