The story of UK onshore exploration goes back to the days of World War I and was prompted by the increasing use of oil for the war effort. The war was drawing to a close as the campaign commenced in 1918. The UK government sponsored the drilling with a budget of £1 000 000 and the work was undertaken by S. Pearson & Sons, a UK engineering company owned by Lord Cowdray (Weetman Pearson). Pearson also had oil interests and he owned the Mexican Eagle Company that had had exploration success in Mexico. Pearson hired a team of American geologists to select suitable drilling locations in the UK. The Carboniferous rocks in the area surrounding the Derbyshire Dome in England and the Midland Valley in Scotland were chosen because of their similarity to the oil-producing areas of Pennsylvania and West Virginia in the USA. Eleven wells were sunk: seven in Derbyshire, two in North Staffordshire and two in Scotland. The first well to be spudded was at Hardstoft in Derbyshire in October 1918 and it was also the first oil discovery. The geological reasoning behind the selection of the drilling sites will be compared with the actual results from 1918–22.