File extension

.xls

Microsoft Excel File Format

.xls files are Microsoft Excel binary spreadsheets: a legacy workbook format using the BIFF record stream inside an OLE Compound File, holding worksheets, formulas, charts, and formatting.

Known meanings

Formats and reference material for .xls

Microsoft Excel File Format

Microsoft Excel File Format (versions 2, 3, 4, 5, 95, 97, 2000, XP)

  • spreadsheets
  • Daniel Rentz
Download

Microsoft Excel File Format (version 2.1)

Microsoft Excel File Format (version 2.1)

  • spreadsheets
Download

Microsoft Office 97 Excel File Format

Microsoft Office 97 Excel file format

  • spreadsheets
  • Microsoft Corp.
Download

Microsoft Excel Binary File Format

Microsoft Excel Binary File Format (unknown version)

  • spreadsheets
  • Mark O'Brien
Download

Compound File Binary File Format

Compound File Binary File Format

  • spreadsheets
  • Microsoft Corporation
Open link

The Chicago Project - GPL Excel project

The Chicago Project - GPL Excel project

  • spreadsheets
  • Charles Wyble
Open link

Java Excel API

Java Excel API

  • spreadsheets
  • Historical
Open link

VB Class to Write an Excel BIFF 2.1 Spreadsheet

VB class to write an Excel BIFF 2.1 spreadsheet directly

  • spreadsheets
  • Paul Squires
Download

OpenOffice.org's Documentation of the Microsoft Excel File Format Versions 2, 3, 4, 5, 95, 97, 2000, XP, 2003

OpenOffice.org's Documentation of the Microsoft Excel File Format Versions 2, 3, 4, 5, 95, 97, 2000, XP, 2003

  • spreadsheets
  • Daniel Rentz
Download

OLE Compound File Format

OLE Compound File (Structured Storage) format

  • spreadsheets
  • Historical
Open link

Details

Format notes

Microsoft Excel Spreadsheet (.xls)

The .xls extension denotes a Microsoft Excel workbook in the binary format that was Excel’s default through Excel 2003. Its data is encoded as a stream of typed BIFF (Binary Interchange File Format) records — describing cells, formulas, shared strings, styles, and worksheet structure — and that stream is stored inside an OLE Compound File (Structured Storage), the same container used by binary Word and PowerPoint documents. It carries the compound-file signature D0 CF 11 E0 A1 B1 1A E1.

A workbook contains one or more worksheets of cells that may hold numbers, text, dates, and formulas, plus charts, cell and number formatting, defined names, and optionally VBA macros. From Excel 2007 the default changed to the XML-based, ZIP-packaged .xlsx (Office Open XML), so .xls is the legacy binary format and .xlsx its modern replacement; older BIFF versions (Excel 2 through 95) also exist and differ from the BIFF8 used by Excel 97-2003.

Preservation And Security Notes

Binary Excel files can embed VBA macros and external data connections, so an untrusted .xls should be treated as potential active content and opened with macros disabled. Spreadsheets are also subject to formula-injection concerns when built from untrusted input. For preservation, migrating cell data and formulas to an open format (Office Open XML, ODF, or CSV for pure data) while keeping the original preserves both the values and the structure.

Further Reading

  • [MS-XLS] Excel (.xls) Binary File Format: https://learn.microsoft.com/openspecs/office_file_formats/ms-xls/
  • OpenOffice.org Excel file format documentation (Daniel Rentz): https://www.openoffice.org/sc/excelfileformat.pdf