As Web-based transactions become an essential element of everyday corporate and commerce activity, it becomes increasingly important for the performance of Web application services to be predictable and adequate even in the presence of wildly fluctuation input loads. In this work we propose a general implementation framework to provide quality of service (QoS) guarantee for cluster-based Web application services, such as E-commerce or directory service, that is largely independent of the Web application and the hardware/software platform used in the cluster. This paper describes the design, implementation, and evaluation of a Web request distribution system called Gage, which is able to guarantee a service subscriber a predefined number of generic Web requests serviced per second regardless of the total input loads at run time. Gage is one of the first, if not the first systems that can support QoS guarantee which involves multiple system resources, i.e., CPU, disk, and network. The fully operational Gage prototype shows that the proposed architecture can indeed provide a guaranteed level of service for specific classes of Web accesses according to their QoS requirements in the presence of excessive input loads. In addition, empirical measure-ment on the Gage prototype demonstrates that the additional performance overhead associated with Gage?s QoS guarantee support for Web service is merely 3.06%.