One of the most important petroleum refining processes -catalytic cracking - was conceived and developed by Eugene J. Houdry in France as early as 1929 but it was after he joined Sun Oil in the USA that it was realised commercially in 1937. This was a period when industrial developments were rapid and with the discovery of rich oil-fields in Saudi Arabia in the 1940s the gradual dominance of an oil-based rather than a coal based economy was emerging. Progress was particularly rapid in the USA with contributions from Ipatieff, Pines, Plank, C.L. Thomas and Haensel. Previously coal hydrogenation had been pioneered in Germany by Franz Fischer and Hans Tropsch to give long chain hydrocarbons and by Friedrich Bergius to give liquid hydrocarbons.