Many efforts in Grid communities have focused on middleware research and development. However, Grid application-level tools are needed which can build higherlevel functionality on top of core middleware services. We work with specific classes of scientific applications and present a Grid-aware toolkit ResGrid for reservoir uncertainty analysis. With the help of the ResGrid, a reservoir engineer can transparently take advantage of Grid resources and services for compute-intensive and dataintensive uncertainty analysis as well as enforce the understanding of multiphase reservoir modeling. This paper explains a typical reservoir uncertainty analysis scenario and evaluates the current limitations a reservoir engineer faces. The ResGrid is introduced in terms of overview, architecture, implementation status. In the case studies, the design and implementation of the ResGrid are verified via a reservoir uncertainty analysis process on the CCT Grid testbed. The ResGrid releases the unbound...