A self-calibrating dissolved gas analysis apparatus and associated method are described. The dissolved gas analysis apparatus includes an analyser having an optical absorption measurement system using one or more electromagnetic energy sources to obtain optical absorption measurements associated with a gas sample. An observed response of the optical absorption measurement system is derived at least in part by using the optical absorption measurement system to obtain optical absorption measurements for a reference gas under one or more distinct moisture conditions. The derived observed response is then processed to quantify deviations between the derived observed response and an expected response and the quantified deviations are used to compensate information associated with gas concentration measurements derived by the dissolved gas analysis apparatus.