Autonomous Underwater Vehicles (AUVs) can be loaded with chemical sensors and sent on missions to conduct high-resolution surveys in the deep sea. They are of interest to the oil and gas industry, as, if fitted with the right sensors, they can be used to help monitor subsea pipelines for leaks and also pinpoint new hydrocarbon reserves under the seafloor by measuring the chemical composition (e.g. the dissolved methane concentration) of the waters above. However, AUVs are prohibitively expensive for routine monitoring and exploration, and often require a large and expensive ship to be present on the surface. A new innovation in AUV technology is the microsub. These miniature AUVs can cost about 2% of the price of a traditional large AUV and are small enough to be launched from a small inflatable boat or the shoreline. They can reach complex areas (shallow waters and reefs) that larger AUVs cannot get to, and can operate in large swarms to efficiently survey a large area. The main drawback of microsubs is that they have limited onboard space and power, meaning that many sensor systems cannot be carried. This means the measurements performed by microsubs are very basic. No methane sensors are currently available that can be deployed on microsubs. At the National Oceanography Centre in Southampton, we have developed a new miniaturised methane sensor that could be deployed on microsubs. In this project, we will adapt this sensor to be deployed on ecoSUB, a microsub developed at the NOC in partnership with Planet Ocean. We will work with BP to test the ecoSUB equipped with the methane sensor on demonstration missions, and help BP to change the way in which they perform leak detection and exploration. Detecting leaks early using microsubs will help BP reduce the cost and environmental impact of subsea pipeline leaks. More efficient exploration will reduce the cost environmental impact of searching for new oil and gas reserves.