.OBI File Extension

File created by Microsoft Outlook, a calendar and email program; contains RSS subscription names and properties in an XML format; used to store RSS feed subscriptions for an outlook profile.

OBI files are named using the convention <profilename>.sharing.xml.obi. They are typically located in the following user directory:
AppData\Local\Microsoft\Outlook.

OBI files can be exported to Outline Processor Markup Language (.OPML) files by selecting the following option in Outlook: File → Import and Export → Export all RSS feeds as OPML file.