The eXtensible Mark-Up Language (XML) developed by the World Wide Web Consortium can be used to develop a framework that improves the interoperability of data in support of marine observing systems. There have been several initiatives investigating how this can be archieved in practice, but to date there has been no strong direction that the marine community should take. This paper presents the findings of an international project tasked with providing such direction. In particular it provides 'pre-standardisation' advice and justification to the international marine community on the use of XML standards for data interoperability. Importently this embraces the very board extent of marine community, covering the very many disciplines and domain areas that exist.