This document specifies a text file format - XML file format - for reporting natural gas analysis results and other data relevant to natural gas. The file name is applicable when it includes the extension of .XML (case insensitive). The XML file format is useful for output from ISO 6974-1[1] for composition and ISO 6974-2[2] for uncertainty, for input for ISO 6976[3] and for input for ISO 10723[4] for performance evaluation. Typically these would be the gas composition as provided on an analysis certificate, or results from a performance evaluation that would be read into an Excel spreadsheet for data processing.