The aim of this research is to investigate the nature of the social and economic transition occurring between the Lapita to post-Lapita periods on the island of Watom, East New Britain Province, Papua New Guinea. Archaeological obsidian from the localities of SAC, SAB, SDI and SDI6 is studied via provenance analysis (PIXE-PIGME and PXRF) and technology analysis, in order to examine the spatial and temporal differences in obsidian source selection and usage.Results from the analysis undertaken revealed continuities and discontinuities in obsidian use between the Lapita and the later transitional periods. Continuity is demonstrated by the consistent use of expedient technology the complete absence of resource maximization during the two periods. Finally, the dominant use of obsidian originating from West New Britain (mainly the sub-sources of Kutau/Bao and Mopir) and the use of Admiralty obsidian (mainly the sub-source of Umrei) as a secondary supply of obsidian were constant over time. Discontinuity between the phases was demonstrated by an increase in the quantity of obsidian transported into the island and the rising dominance of West New Britain obsidian (especially the Mopir sub-source) in the transitional phase.From the results summarized above, it was argued that changes in social distance and/or exchange relationships occurred over time. That is, while the communities on Watom Island maintained exchange relationships with groups in the direction of the Admiralty Islands during the later periods, they had closer social ties with those in the West New Britain source region. Furthermore, the presence of a highly concentrated distribution network of Mopir obsidian within the localized region of Watom and the Duke of Yorks during the transitional phase was proposed. The existence of this localized network raises the possibility of regionalization taking place, and also suggests a close social relationship between communities from the two locales.