An Internet enabled, business-to-business computerized transaction system is disclosed in its preferred embodiment for use in providing rental car services for high volume users and comprises an Internet web portal through which the high volume user may access a plurality of service providers including an integrated business computer network for at least one rental vehicle service provider. The rental vehicle services provider computer network is configured to interconnect a geographically diverse plurality of branch offices, cataloguing their available rental vehicles and schedules for same as well as handling all transactional data relating to its business. The Internet web portal provides ubiquitous connectivity and portability for a multi-level business organization who regularly places high volumes of rental purchases with its business partner and also those other service providers who may or may not have the same integrated business computer system and software. Utilizing the method and apparatus of the present invention large volumes of rental transactions may be placed, monitored, altered during performance, and closed out with financial accounting and payment being made virtually without human intervention.