A Web service designates a new type of software component having the capacity to publish its functions on the Internet in the form of services, and to make these services easily invocable and to make them available to clients through standard Internet protocols. However, Web services as they are presented are limited to simple functionalities, so the task of composing existing Web services is essential in order to satisfy a complex request of clients. In this work, we proposed a model for the performance evaluation of a Web services system based on an open tandem queue network, with three stations, taking into account client requests. An analysis and modeling of this system with a Jackson network is reported. We calculated the average response time in the system, the average number of clients in the system, the average number of clients waiting in the system, and the average waiting time as a function of \(\lambda \) .