Tracing resource usage by Grid users is of utmost importance especially in the context of large-scale scienti c collaborations such as within the High Energy Physics (HEP) community to guarantee fairness of resource sharing, but many dif culties can arise when tracing the resource usage of distributed applications over heterogeneous Grid platforms. These dif culties are often related to a lack of interoperability of the accounting components across middlewares. This paper brie y describes the architecture and workow of the Distributed Grid Accounting System (DGAS) [1] and evaluates the possibility to extend it with a Resource Usage Service (RUS) [2, 3] interface according to the Open Grid Forum (OGF) speci cation that allows to store and retrieve OGF Usage Records (URs) [4, 5] via Web Services. In this context the OGF RUS and UR speci cations are critically analyzed. Furthermore, a prototype of a RUS interface for DGAS (DGAS-RUS) is presented and the most recent test results towards a full interoperability between heterogeneous Grid platforms are outlined.