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Andesitic magma erupted at island arc strato-volcanoes is stored in the shallow crust prior to eruption. Constraining the size, location and characteristics of magma reservoirs is key to forecasting the likelihood and characteristics of future eruptions. The island of Montserrat, in the Lesser Antilles, has been the subject of an active-source seismic tomography experiment (the SEA-CALIPSO experiment) with the main aim of studying the magmatic system of the active Soufriere Hills Volcano (SHV). We present the results of the three-dimensional travel-time inversion of the dataset. We are able to image the main features of the volcanic system of the island including SHV and the two older and extinct volcanoes. The shallow structure is dominated by the presence of high-velocity cores beneath the three volcanic centres. Beneath SHV at depth between 5 and 8 km we observe a negative velocity anomaly (NVA) roughly 4 …