This paper proposes a flexible transactional behavior model for services coordination. We assume that given a flow describing the application logic of a service based application, it is possible to associate to it a personalised transactional behaviour in an orthogonal way. This behaviour is defined by specifying contracts and associating a well defined behaviour to the activities participating in the coordination. Such contracts ensure transactional properties at execution time in the presence of exceptions. Keywords: Transactional behaviour, advanced transactional models, services oriented systems, services based applications, web services.