Google added OpenDocument format to the list of supported documents. OpenDocument is supported by important office suites like OpenOffice.org, Star Office, KOffice, but also by Google Docs & Spreadsheets. OpenDocument can be used to store many kinds of files, including documents (.odt), spreadsheets (.ods) and presentations (.odp).
Google's filetype: operator allows you to restrict the search results to files that have a specific extension. This table shows the number of files from Google's index for Open Office and Microsoft Office:
| File types || Open Office || Microsoft Office |