Microsoft Excel Binary File Format

File extension: .xls Developed by: Microsoft Type of format: Spreadsheet MIME: application/vnd.ms-excel
Microsoft Excel up until 2007 version used a proprietary binary file format called Excel Binary File Format (.XLS) as its primary format. Excel 2007 uses Office Open XML as its primary file format, an XML-based format that followed after a previous XML-based format called "XML Spreadsheet".