Abstract: A method of base metal exploration in sedimentary rocks which depends on detecting anomalous amounts of the light hydrocarbon gas methane in the host rocks has been applied in a number of orientation surveys in the British Isles and in Europe. The results of these studies are described, and the limitations of the method discussed. It is suggested that the principal difficulty lies in the extraction technique which is based on heating, and alternative methods are proposed. The preliminary results from these new methods are discussed and compared with those from the original study. A number of the samples analysed by the new methods are calcites of differing diagenetic origins. It is postulated that the differences in methane found in these samples may give a clue to the organic geochemistry of the rocks at the time when the calcites were deposited.