Per Release 18 Patch Release Notes 018.020.005FP (1220.0.05), it is 20 MB.
File Size Limit Increase
The file size limit for Oracle CRM ON Demand has been increased from 9 MB to 20 MB. The 9 MB limit
referenced in the following Release 18 Online Help topics should be 20 MB.
• Attaching Files and URLs to Records
• Attaching Files to Records through Attachment Fields
• Importing Your contacts
• Import and Export Tools