Abstract. Web Services offer a widespread standard for making services available on the Internet. Of particular interest is the possibility of composing existing distributed services to create new complex ones. Existing research has already studied long running transactions within a formal context. In this other research, compensations are just partly compositional: a transaction’s failure triggers the compensation of immediately enclosed transactions, but not those of nested transactions. In this paper we formally model a more compositional protocol with the asynchronous pi calculus. The resulting behavior is similar to that of the Business Transaction Protocol of OASIS [1], which also has arbitrary nesting.