Coastal trading or exchange systems were widespread in recent Papua New Guinea history. Obsidian from the three major known sources-Lau and Pain Island in the Admiralty Group, Talasea in New Britain, and Ferguson and Dobu Islands off the eastern tip of papua-has been included in this trade. The chemical composition of rhyolitic obsidians from different sources is discussed as are the 2, 000-3,000 year old artifacts from Watom Island and their relationship to Lapita pottery from New Caledonia. See also AATA 15-984 and 19-1064 for further obsidian studies. -- AATA