A uniform button for the Commonwealth Oil Refineries company (COR) by Stokes and Sons, Melbourne.
Thanks to Wikipedia: The Commonwealth Oil Refineries ran between 1920-1952 as a joint venture by the Australian government and the Anglo-Persian Oil company. Billy Hughes initiated the partnership. In 1924 the first Australian refinery opened near Laverton. The Menzies government sold their interest in 1952 to the Anglo-Iranian Oil Company, which in 1954 become the British Petroleum Company (BP). The brand COR was continued until 1959.