This report is a contribution to the Strategic Environmental Assessment (SEA6) conducted by the Department of Trade and Industry (now Department of Energy and Climate Change). The study area dealt with in this report includes all of the Irish Sea that falls within Irish Jurisdiction. The report is intended to complement a similar study of UK waters in the Irish Sea undertaken as part of the UK Government's Strategic Environmental Assessment (SEA6). The aim of this report is to present an up-to-date overview of all relevant data concerning methane-derived authigenic carbonate and features associated with shallow gas and seabed fluid flow in the Irish sector of the western Irish Sea. It presents a detailed assessment of potential gas sources and migration pathways, shallow gas, gas-related seabed structures and evidence of present day gas seepage in the study area.