Rotary energy exchangers are used in heating, ventilation and air-conditioning systems to transfer heat and moisture between exhaust and supply air streams, thereby reducing the energy consumption of a building. As heat and moisture are being transferred between supply and exhaust air streams, there is a risk that gaseous contaminants may also be transferred through the energy wheel. Previous studies found that the amount of contaminants that are transferred is affected by the operating conditions, properties of the contaminants and the properties of the materials used in the exchanger. In this study the effect of concentration of the contaminant as well as the mixture of multiple contaminants present in the air is investigated. The results show that the exhaust contaminant transfer ratio may be affected by the concentration of the contaminant in the airstream for some contaminants. For isopropanol, a 15% decrease in exhaust contaminant transfer ratio was observed when the concentration increased from 9 to 48 ppm. However, for methanol, the average exhaust contaminant transfer ratio was 51% with a standard deviation of ±1% over the range of 15 to 48 ppm, showing no significant change in transfer with concentration. Finally, the exhaust contaminant transfer ratios remained unchanged when isopropanol and methanol co-existed in the airstream.