United States: EPO Practice - Priority Pitfalls In European Patent Applications Based On U.S. Priority Applications

Article 87 of the European Patent Convention (EPC) allows applicants for European patent applications to claim the benefit of the filing date ("priority date") of an earlier application ("priority application") under certain conditions.  While Article 87 EPC broadly corresponds to Article 4 of the Paris Convention, the European Patent Office's (EPO) implementation of Article 87 EPC can lead to denial of priority claims and, ultimately, loss of applicant's rights.  Without careful attention by practitioners, claiming the benefit of a U.S. priority application may result in loss of rights. 

The EPO Enlarged Board of Appeal (EBA) specifically considered the interpretation of Article 87 EPC in its decision G2/98.  The following key points arise when claiming priority under Article 87 EPC:

  1. The European application must be for the same invention as the priority application, and  
  2. The priority application must be the first application for protection of the invention and must not be filed more than twelve months before the European application's filing date. 

Although the EPO does not routinely examine priority claims, to avoid the risks of improperly claiming priority—and detrimentally relying on invalid priority claims—practitioners should carefully assess the contents of the priority application and European application before filing to ensure the claimed priority is valid.1  Further, during prosecution of the European application, practitioners should cautiously amend the European claims to maintain the valid priority claim.  Scenarios exemplifying some common priority pitfalls are discussed below. 

Priority Claims to the "Same Invention"

According to the EBA in G2/98, the EPO acknowledges priority claims for the "same invention" "only if the skilled person can derive the subject-matter of the claim directly and unambiguously, using common general knowledge, from the previous application as a whole."2  Thus, the EPO priority standard requires not only that all elements of a claim be explicitly or implicitly disclosed in the priority application, but that any claimed combination also be so disclosed.  This standard is the same applied to determine the validity of added subject matter by amendment under Article 123(2) EPC.3  Simply stated, if a claim could not be added to a priority application without contravening Article 123(2) EPC, it cannot validly claim the priority date. 

  1. Claiming Priority to a U.S. Provisional Application Filed Without Claims

U.S. provisional applications can be filed without claims, and in some cases with as little as a single drawing.  Although these applications qualify as potential bases for priority under Article 87(3) EPC, they routinely fail to provide valid priority dates for claims generalizing their specifically disclosed features.  Even the EPO's "whole contents" approach in Article 88(4) EPC, which recognizes that priority may be granted for subject matter disclosed but not claimed in the priority application, offers scant assistance in establishing priority.

Indeed, EPO practice under Article 123(2) EPC routinely denies broadening amendments such as attempts to define a range based only on a series of discrete values or introducing generalized terms from discrete example (e.g., broadening "diesel engine" to "combustion engine").  Without any claims or statements corresponding to claims in the priority application, the claims added to the European application often cannot be clearly and unambiguously derived from the priority application. 

  1. Claiming Priority to a U.S. Provisional or Nonprovisional Application Filed with Very Broad Claims

Including only very broad claims in a priority application does not guarantee the priority of narrower claims falling within their scope.  A priority application that recites, for example, a range or a genus does not necessarily support narrower claims presented in the European application because the range or genus claim in the provisional application cannot be separated into a narrower subgenus or species without supporting direct and unambiguous disclosure in the application as filed.4

  1. Claiming Priority to a U.S. Provisional or Nonprovisional Application Filed with Very Narrow Claims

The analogous case involving only narrow claims can have similar problems.  Although the specific claims and examples may be sufficient to support a broader claim, without the unambiguous disclosure of the broader claim scope, no valid priority may be claimed.    

As seen in each of the three preceding scenarios, either the lack of corresponding claims or the lack of disclosure providing direct and unambiguous derivation of the claim scope can be fatal to a priority claim in a later European application.  When filing an application that is to serve as a basis for priority, practitioners must consider providing a proper basis for later claims at the EPO. 

Practitioners may avoid the traps in the preceding scenarios by incorporating language that closely resembles future claim language in a claimless provisional application, including alternative embodiments and definitions of subgenus and species falling within the scope of broad claims, and unambiguously disclosing broader claim scope in priority applications with narrow claims.   

Priority Claims to the "First Application"
European applications claiming priority to U.S. continuation-in-part (CIP) applications raise unique questions of priority under Article 87(1) EPC regarding the "first application" for protection of the claimed invention.  Because CIP disclosures include content from an earlier parent application and later new matter, valid priority claims turn on whether the European application claims relate only to the new matter in the CIP.5  The critical point when analyzing the validity of a CIP priority claim is to determine if the CIP is the first application to disclose the invention claimed in the European application.6 

  1. Support for the European Application Claims Only Found in a CIP

A European application properly claims priority to a CIP where the European application claims relate solely to new matter contained in the CIP (i.e., cannot be derived from the parent application).  The CIP is the first application for the invention of the new matter according to Article 87(1) EPC. 

  1. CIP New Matter Is an Example Wholly Encompassed by the Parent Application

Where the CIP's new matter does not add a new element to the invention covered by the parent application, the parent application remains the "first application" disclosing the invention claimed in the European application.  As such, the parent application alone supports a valid priority claim. 

A priority claim to the CIP may be valid, however, if a dependent claim in the European application cannot be derived from the parent application alone.    

  1. European Application Claims Read on Subject Matter of Parent Application

As in scenario 2, a European application cannot validly claim priority to a CIP when the European claims read on the subject matter of the parent application.  The "first application" to disclose what the European application claims recite is the parent application. 

These three scenarios are particularly relevant where the parent application was filed more than twelve months before the European application.  Outside of this priority period, and when the European application's claims are not entitled to the CIP's priority date, the claims take the filing date of the European application.  Any disclosures made before the European application's filing date can be used to attack the validity of the claims, including disclosures made by the applicant and publication of the parent application.  A parent application published after the filing date of the European application by the EPO or as a PCT application may still qualify as prior art for novelty purposes under Article 54(3) EPC. 

Under these circumstances, practitioners may avoid risking the validity of a European application due to an invalid priority claim to a CIP by only reciting claims that are exclusively based on the CIP application.

Amendments During Examination

Even after ensuring that a European application as filed contains a valid priority claim, applicants risk losing the claimed priority during prosecution through claim amendments.  To maintain the claimed priority, practitioners should consider the content of the priority application and attempt to introduce amendments that are clearly and unambiguously supported in the priority application. 


The EPO's strict priority standard means that practitioners must pay close attention to the preparation of the priority application so it can adequately support potential claims that may be envisaged.  Failure to secure proper priority may leave an application vulnerable to the applicant's own disclosures.


1 Where an application is filed under the Patent Cooperation Treaty (PCT), the PCT filing date is taken as the filing date under the EPC and not the date of entry into the European regional phase.

2 Enlarged Board of Appeal in G2/98, [2001] OJ EPO 413, 433.

3 Art. 88(4) EPC (recognizing priority claims to any matter disclosed in the priority application, not just to the claims of a priority application); Guidelines for Examination F.VI, 2.2.

4 Guidelines for Examination F.VI, 2.2.

5 Id. at F.VI, 2.4.4.

6 See id.; id. at F.VI, 1.4.1.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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