An increase in oxygen consumption was observed in healthy male subjects breathing argon-containing gas mixtures during physical exercise. According to a detailed analysis of the methodology and calculations, this effect exceeded the possible errors in the measurements. It was proposed that argon has a catalytic effect on the kinetics of oxygen consumption as an attempt to explain two of its known effects, i.e., an increase in oxygen consumption in human subjects breathing moderately hypoxic gas mixtures and an increase in the survival rates observed previously for rats in acute hypoxia.