Periodic analysis of heat-transfer fluids (HTFs) is among the most neglected practices in industrial settings. But over time in operation, HTFs can and do accumulate contaminants from the heat transfer system and also undergo chemical changes that negatively affect the performance of the system. Regular analysis of HTFs allows processors to promote efficient long-term operation of heat transfer systems and avoid problems that require extensive maintenance. This whitepaper provides information to help improve understanding of how and where HTFs break down within the system, allowing processors to identify potential issues early, when adjustments can be made to the operation to prolong the life of the fluid.