As this graph shows, after the expansion of the late 19th century, the growth of coal production slowed in the interwar years before rising to 3 million tonnes in 1960. The growth, where it occurred, came mainly in the Waikato (North region) coalfields, as the West Coast fields suffered from the increasing use of oil in shipping, which had been their major market. The nationalisation of the mines by the Labour government in the early 1940s saw an increasing proportion of coal being produced by the state.