Minerals magnetics has been proposed as a means of improving our understanding of petroleum systems. We have carried out extensive rock magnetic experiments on core samples from the Tertiary reservoir sands of the Bittern and Pict Field, UK Central North Sea. This together with Petroleum Systems Modelling/Analysis has revealed the potential to characterise hydrocarbon migration pathway and fill-pattern through siderite identification. We have also suggested a plausible mechanism responsible for these observations. Furthermore, the presence of different flow zones or ‘compartments’ in petroleum reservoirs may also be identified through the distribution of magnetic minerals. In terms of ease of application in oil exploration and reservoir characterization, there is a potential to define this parameter very efficiently through the measurement of magnetic susceptibility.