While service-oriented architecture (SOA) is gaining momentum in research and industry, we believe the field of methods for designing information systems according to SOA still leaves room for improvement. Nevertheless, the implementation of SOA design principles demands a methodical approach. All existing methods have shortcomings of some kind, but also propose some useful concepts. In this paper, the SOA method (SOAM) is presented. It is based on an understanding of the useful concepts from existing methods and puts them together with new ideas that address the key shortcomings. It has been tested in practice at Vattenfall Europe, one of the largest European energy and heat providers and three other companies. The evaluation has shown that SOAM is well-defined, supports the design of information systems according to the SOA design principles and can be applied in practice.