Recent instances of counterfeit refrigerants causing violent and unexpected explosions, resulting in multiple fatalities, have been reported in mobile refrigeration units around the world. In addition, counterfeit refrigerants have caused system reliability issues in numerous air-conditioning applications. It was initially believed the inclusion of methyl chloride (R-40) in the refrigerant composition caused these explosions and reliability issues. Further investigations have revealed that the counterfeit refrigerants contained other chlorinated gases both with and without R-40. These results indicate that the counterfeit refrigerant problem may encompass more than just the issues surrounding R-40. This paper will describe various failure investigations, the composition of counterfeit refrigerants and the steps to follow to detect counterfeit and contaminated refrigerants. In the future, if and when the cost of refrigerants increases, the HVAC&R industry and refrigerant supply chains will have to be vigilant in their monitoring, otherwise counterfeit and contaminated refrigerants will become more common in the marketplace.