XML is currently being used as the message syntax for Web services. To enable small mobile devices to use Web services, this XML use must not be too resource-consuming. Due to several measurements indicating otherwise, alternate serialization formats for XML data have been proposed. We present here a format for XML data designed from the ground up for the mobile environment. The format is simple, yet gives acceptable document sizes and is efficiently processable. An automaton-based approach gives further improvements when full or partial schema information is available. We provide performance measurements verifying these claims and also consider some issues arising from the use of an alternate XML serialization format. Key words: XML and Semi-structured Data, Web Services, Mobile Environment, XML Serialization Format, Binary XML