In R 5/08 the Enlarged Board stated it was clear that apart from any reasons accepted by the Enlarged Board as special enough to justify the submission of additional facts, arguments or evidence, the petition itself must be adequately substantiated. R. 107(2) EPC requires a petition to indicate the reasons for setting aside the decision of a board of appeal and the facts and evidence on which it is based. This corresponds to the similar provisions requiring substantiation of an opposition or an appeal (R. 76(2)(c) and R. 99(2) EPC). The contents of a petition must be sufficient for the petitioner's case to be properly understood on an objective basis and must enable the Enlarged Board (and any other parties) to understand immediately why the decision in question suffers from a fundamental procedural defect. The petition must thus set out the reasons why it requests that the impugned decision be set aside, specify the facts, arguments and evidence relied on and must do so within the time limit for filing the petition, namely two months after notification (see Art. 112a(4) EPC; see also R 4/13, R 17/13, R 3/18).

In R 9/10 the Enlarged Board held that an implicit request to set aside the decision was sufficient. In R 20/10 the Enlarged Board stated that the obligation to file a reasoned statement could not be construed so narrowly as to mean that any kind of reasoning was sufficient to fulfil this requirement, as long as it was extensive enough. In R 2/08 the Enlarged Board held that for the petition to be admissible, it was however sufficient if only one ground was sufficiently reasoned in the request, just as it is for an appeal or opposition (see also G 9/91, OJ 1993, 408).