There is a great deal of confusion floating about when it comes to selecting gas mixtures for analytical applications. Questions such as "How is the gas certified?," "What standard should I use?," and "What level of uncertainty is acceptable?" are common concerns heard among those tasked with specifying and using mixtures. In addition, the uncertainty regarding terminology, measurement, safety, and storage can make specifying mixtures a true source of headaches and hassles for any lab manager. The following article provides answers to questions about gas mixtures.