The P2P service-oriented environment presents new opportunities and challenges for distributed computing and resource sharing. In this paper, we present a middleware infrastructure, called CCSD, for decentralized service discovery in a wide-area ad hoc P2P service-oriented environment. Two of the key ideas of a CCSD P2P network are: 1) The concept of context awareness is extended to the awareness of service capacities of P2P peers, by which peers are able to understand and compare each other?s service capacities; and 2) A peer?s capacity context description is replicated in several designated peers in addition to the peer itself. Using a hash table, the description of the most suitable capacity context for a service request can be located quickly and the service request is forwarded to and served at the peer associated with that capacity context. CCSD, designed to satisfy the dynamic and constrained nature of the ad hoc P2P environments, benefits service users in the environments by providing the most suitable service capacity transparently.