Since early works, web servers have been designed as parallel applications to process many requests at the same time. While web service based applications are performing more and more, larger and larger transactions, this parallelization culture still not reached the client side. Business to Business (B2B) applications are becoming intensive users of web transactions through Service Oriented Architecture Standard. As multicore systems are now widely available, parallelization seems the right way to fit the need of such applications. In this paper, we describe an API based on OpenMP for transparently parallelizing web service calls, i.e. the serialization, deserialization and connection processes. Our API is mainly based on a software pipeline which splits web service calls into several tasks. Both synchronous and asynchronous modes can be used with this API to call web services. We present experimental evidence demonstrating the ability of our API to achieve high level performance.