Next-generation applications based on Web services impose additional requirements on the use of coordination protocols with various optimizations, such as the two-phase commit protocol (2PC). This paper analyses the well-known 2PC optimizations presumed commit and presumed abort, and presents an improved 2PC that is suitable for Web services based applications. More specifically, the protocol allows every individual service provider to choose dynamically the most appropriate presumption for any distributed transaction. The protocol does not introduce extra overhead to the previous 2PC variants in terms of number of messages and log records, and it is easy to understand and realize.