Abstract: A computerized system for registering participants for a service provided in a plurality of events for which a variable number of participants may be registered and where at least a part of the costs of the event are fixed. The system receives registration data providing a first and a second number of participants to be registered for the event. The system registers the participants for the event and conducts at least two transactions. The first debiting a first account for, at least, the fixed costs; the second crediting the first account by a further amount in dependence on the registration of said second number of participants for the event.