The CORA (Coallocative, Oversubscribing Resource Allocation) architecture is a market based resource reservation system that utilises a trustworthy Vickrey auction to make combinatorial allocations of resources. This paper provides an overview of several significant components of the CORA architecture. Firstly, CORA utilises a novel combination of techniques to improve utilisation, including oversubscription, coallocation, just-in-time reallocation and a flexible contract structure. Secondly, this paper utilises a new auction architecture that does not require the auctioneers to be trusted. The advantage is that any entity (untrusted or otherwise) can conduct a privacy preserving Vickrey auction, removing the need for a trusted and privileged auction service within the system. CORA demonstrates how a practical, efficient and trustworthy auction scheme can be implemented in a Grid Economy.