We present an extension of the PEWS language, named PEWS-CT1, for reliably composing web services using contracts. The expression of contracts adds non functional properties to service compositions. A PEWS-CT program defines the behaviour of a compound web service as the combination of individ- ual operations and conditions for expressing non-functional and temporal con- straints. Therefore, a new runtime system for the language has been specified, taking into consideration the verification of contracts and temporal conditions.