Business Transactions can be seen as a hierarchy of tasks, in which execution is orchestrated in order to manage the different interactions among implied services. Business Transactions are generally long running, consisting of sub-transactions that may fail or be cancelled. In addition, the problem also entails concurrent access to data available via Web services. There are many solutions, namely compensation and locking, as present in the "DBMSs" transactional model adapted to Business Process model. The locking restricts access and degrades the Quality of Service. Compensation can be complicated to implement and costly in terms of performance. Each one of these solutions has a cost. In this paper we propose a cost model for strategies based on locking and on compensation to compare them in the execution plan of a Business Transaction. This comparison allows us to choose the least expensive strategy.