The Otway Project in Victoria, Australia, run by the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) began injecting gas (80% CO2: 20% CH4) in a supercritical state in April, 2008. It has been labeled with tracers (SF6, Kr and CD4) added via a purpose built slip-stream injector to unequivocally allow verification of the presence of the injected CO2 at various monitoring sites. A bottom-hole assembly installed in the Naylor-1 monitoring well enables multi-level sampling of fluids at reservoir pressure to allow the determination of hydrological and geochemical processes that control plume movement and water-rock- CO2 interactions in the subsurface.