Current BPEL engine products are difficult to meet the highly concurrent demands of increasing mission critical business processes application. The authors follow the ideas of SEDA and propose a new architecture for high-concurrency BPEL engine, which they call SEDA4BPEL. In SEDA4BPEL, the implementation of BPEL related web services protocols is encapsulated into four primary event-driven stages, to provide independence, isolation and modularity. They also introduce two controllers to manage excessive concurrent process instances. They present the SEDA4BPEL design and the implementation of a BEPL engine based on this architecture.