Reports, images, GIS and gridded products describing the Palaeozoic geology and conventional petroleum systems of parts of the UK offshore. Devonian and Carboniferous rocks are the focus in and around the Mid North Sea High, Central North Sea, the Moray Firth and Orcadian Basin. In the greater Irish Sea area, Carboniferous rocks are described. The peer-reviewed products were produced for the 21CXRM Palaeozoic Project by BGS for DECC/OGA, Oil and Gas UK and oil company sponsors between November 2014 and May 2016, to improve regional digital datasets and knowledge of the underexplored Palaeozoic petroleum systems, and to stimulate exploration. The petroleum systems analysis was based on new interpretations of extensive well, seismic, gravity-magnetic and source rock datasets, integrated with petrophysical studies, basin modelling and UK onshore knowledge. Released data were collated and interpreted, and interpretations of unreleased data were included with agreement of the data owners. Unreleased raw data is excluded, as is the UK Government Seismic data released in 2016. The datasets are applicable for use at scales between 1: 750,000 to 1: 3,000,000.