The WTO Agreement on Government Procurement (GPA) is a plurilateral Agreement, meaning that it comprises only a subset of the full Membership of the WTO. Currently, a number of WTO Members that are not Parties to the Agreement either are actively seeking accession to it, have commitments to accede to the GPA in their respective WTO accession protocols or are, on their own initiative, looking at the potential pros and cons of accession. In this context, there is a need for factual information concerning the potential consequences of GPA accession, and a framework to assess related benefits and costs. Of interest is both the systemic value of such accessions-i.e. the value they will add to the extent of market access commitments under the Agreement-and their potential benefits and costs for individual acceding Parties. This Working Paper introduces new sources of information relevant to these topics (principally, the statistical reports that have been circulated recently by GPA Parties) and shows their relevance to and usefulness in assessing the above-noted matters. The Paper presents estimates of the size of potential market access gains from pending and possible future GPA accessions, based on simple extrapolations from the data sources identified. Next, the Paper shows how the same data sources can assist in throwing light on the potential benefits and costs of GPA accession for individual WTO Members/countries contemplating accession. The latter use of the data is developed in the context of a more general discussion of the benefits and costs of GPA accession for individual WTO Members, also drawing on existing literature, qualitative aspects and "insights from the field" (i.e. our own work in advising and conducting seminars for such countries and other WTO Members).