||A compact plug-n-play methane sensor designed to measure partial pressure of methane gas (pCH4) dissolved in liquids. It is designed for applications such as the detection and monitoring of oil spills, the study of anoxic conditions, determining the effects of fracking, methane hydrate studies, and more. The instrument also measures total dissolved gas pressure (TDGP). The instrument can be immersed in water, oil or water-oil mixtures, and its titatnium housing is rated to 6000 m (600 m for plastic housing). The intrument operates via infra-red detection, and offers an optional copper antifouling head to reduce biofouling, plus other optional additions such as battery packs, locking pigtail cables and mooring frames. The intrument measures pCH4 within the range of 0-1 % by volume (~0-300 μg/L; by mass), to an accuracy +/- 2 % of maximum range. The instrument measures TDGP from 0-2000 mbar to an accuracy of +/- 1 %. The instrument has an equilibrium rate of 8 minutes (with water-pumped head), a sample rate of 2 seconds, and has an overall resolution of 0.1 % of maximum range.