With the recent advances in Internet and mobile technologies and infrastructures, there are increasing demands for ubiquitous access to tourist information systems for service coordination and integration. However, disparate tourist information and service resources such as airlines, hotels, tour operators, etc., make it difficult for tourist to use them effectively when planning their trips and/or during their trips. Motivated by the emerging technologies of Multi-Agent Information System (MAIS) and its ability to aid Internet and mobile users, together with semantic Web that can effectively organize information and service resources. In this paper, we propose a Virtual Travel Agent System (VTAS), which is built upon these technologies. In this paper, we formulate a scalable, flexible, and intelligent MAIS architecture for VTAS with agent clusters based on a case study of a large service-oriented travel agency. Agent clusters may comprise several types of agents to achieve the goals of the major processes of a tourist?s trip. We show how agents can make use of ontology from the semantic web help tourists better plan, understand, and specify their requirements. We further illustrate how this can be successfully implemented with Web service technologies to integrate disparate Internet tourist resources.