New file extensions and file formats for Excel Spreadsheets based on Open XML data format. XLSX file format was introduced with Microsoft Excel 2007. XLSX files uses ZIP compression for smaller file sizes. The 2007 Microsoft Office system continues with this transition by adopting an XML-based file format for Microsoft Office Excel 2007, Microsoft Office Word 2007, and Microsoft Office PowerPoint 2007. The new file format, called Office Open XML Formats, addresses these workplace issues with changes that affect the way that you approach solutions based on Microsoft Office documents.