What is the difference between unavoidable and unintentional delay in patent application abandonment?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The MPEP 711.03(b) distinguishes between unavoidable and unintentional delay for reviving abandoned applications:

• Unavoidable delay (37 CFR 1.137(a)): This requires a higher standard of proof. The delay must have been unavoidable despite the exercise of due care and diligence.
• Unintentional delay (37 CFR 1.137(b)): This has a lower standard and is more commonly used. The delay must have been unintentional, but doesn’t require proof of due care and diligence.

The type of delay affects the petition requirements and fees for revival. Unintentional delay petitions are generally easier to file and more frequently granted.