A order matching system which allows users to define and modify buy/sell order schedules for execution within one or more transaction destinations. The system uses order schedules and associated evaluation heuristics to evaluate and update order characteristics such as price and quantity based on user-specified criteria. The matching system comprises a user interface which can be connected over the internet to various transaction destinations through a schedule manager and a transaction order interface. The user interface provides users with the ability to obtain information concerning the status of their order account as well as the ability to enter or modify their order schedules. The order manager uses a schedule supervisor server to maintain a database containing order schedules and order status information and to execute variable evaluations on the basis of these order schedules and associated evaluation heuristics. The order manager also uses a transaction supervisor server to monitor the status of order fills and to update the database periodically. The transaction order interface receives and communicates information messages between various transaction destinations and the schedule manager. In this way, the order matching system allows users to specify the ways that various terms and conditions at which they are willing to transact may change over time in an automated fashion while still retaining the ability to intervene at any time.