Inter partes reviews (IPRs), ex parte reexaminations and post-grant reviews (PGRs) are all post grant proceedings offered by the United States Patent and Trademark Office (USPTO) that allow parties to challenge the validity of a patent.

Each procedure possesses its own advantages and considerations. To determine which to use, a patent owner or challenger should consider several factors, such as the nature of the dispute, the availability of prior art, and the desired level of involvement from the owner or challenger.

Here are a few key differences:

1. Parties involved: In an IPR or PGR, a third party files a petition to challenge the validity of a patent, and both the challenger and the patent owner can participate in the proceeding. In an ex parte reexamination, anyone can request reexamination of a patent, but only the patent owner has the opportunity to participate in the reexamination process.
2. Standard for institution: In an IPR or PGR, the petition must demonstrate a reasonable likelihood that at least one claim is unpatentable. In an ex parte reexamination, the petition must demonstrate there is a substantial new question of patentability.
3. Standard of review: In all three proceedings, the standard of review is whether at least one claim is more likely than not unpatentable. This is different than the clear and convincing standard used in district court.
4. Timing: An ex parte reexamination may be requested at any time during the life of the patent. A PGR petition must be filed within the first nine months following the patent grant. An IPR petition may be filed any time after the nine month mark following the patent grant, but must be filed within twelve months of being served with any complaint alleging infringement of that patent.
5. Scope of petition’s grounds: In an IPR or ex parte reexamination, the petition is limited to anticipation and obviousness arguments based on patents and printed publications. In a PGR, the petition may also include written description, enablement and indefiniteness challenges.
6. Scope of review: In an IPR and PGR, the scope of review is limited to the grounds and prior art asserted in the petition, while in an ex parte reexamination, the USPTO can consider any prior art that raises a substantial new question of patentability.
7. PTAB involvement: IPR and post-grant proceedings are heard before the PTAB, while an ex parte reexamination is conducted by the USPTO's Central Reexamination Unit, which may thereafter be appealed to the PTAB.

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