A new method of measuring hydrogen sulphide concentrations in gas streams, suitable for SAGD operations, is reported. The method is independent of the steam content up to 70 mole %, the composition, temperature and pressure of the gas, and has been tested and validated in the field. The method has a standard error of about 5%. By contrast, the stain tube (Draeger) measurements performed routinely on various gas streams at SAGD pilots are shown to be correct only within an order of magnitude of the reading by the new method. Factors between two to ten were common between stain tube readings and the corresponding true readings taken immediately after or before the stain tube readings. The results have implications for plant safety procedures. It is suggested that certain plant streams be sampled only by operators wearing self-contained breathing apparatus; stain tube readings of the past have suggested this to be not necessary. There are further implications for understanding of partitioning of produced hydrogen sulphide in process streams.