In T 877/90 an oral disclosure was regarded as having been made available to the public if, at the relevant date, it was possible for members of the public to gain knowledge of its content and there was no bar of confidentiality restricting their use or dissemination of such knowledge (see also T 838/97).

Where a written disclosure was published which was based on an oral disclosure at a public conference held some years earlier, it could not as a rule be assumed that the written disclosure was identical to the oral disclosure. Additional circumstances had to be put forward and proven to justify that conclusion (T 153/88). In T 86/95, the board assumed that the disclosures were identical since it was highly unlikely that the speaker would have passed over such a salient feature at the conference.

In T 348/94 the board confirmed that a written publication allegedly based on a paper previously read at a public meeting held some time earlier (in this case ten months) could not be assumed to be identical to what was orally disclosed, and might contain additional information. As to the extent of the oral disclosure, the burden of proof remained with the opponent.

In T 1212/97 the opponent had submitted that the invention had been made available to the public at a lecture given some days before the priority date to an audience of some 100 to 200 persons. The question to resolve was whether there was any safe and satisfactory evidence regarding the content of what had been made available to the public at the lecture. The board did not consider evidence from the lecturer alone to be satisfactory evidence as to what had been made available to the public at the lecture. Even an audio or video tape recording made of the lecture, unless publicly available, would have to be treated with caution, if several hearings or viewings were necessary to extract all the information. Information appearing in each of the contemporary written notes made at the lecture by at least two members of the audience could usually be regarded as sufficient, whereas information in the notes of a single member of the audience might be inadequate, as it reflected the thoughts of the listener rather than solely the content of the lecture. If the lecturer read his lecture from a typescript or manuscript, or the lecturer wrote up his lecture subsequently, and the lecture was subsequently published in that form as part of the proceedings, then the written version might be taken as some evidence of the contents of the lecture, though with some caution as there would be no guarantee that a script was completely and comprehensibly read, or that a write-up had not been amplified. Most useful would be a handout given to the public at the lecture, containing a summary of the most important parts of the lecture and copies of the slides shown. None of those types of evidence were available in this case (see also T 1057/09, T 428/13, applying the principle, stated that the affidavit of the lecturer was not sufficient to give proof what was actually disclosed orally).

In T 2003/08 of 31 October 2012 date: 2012-10-31 the board observed that, in contrast to a written document the contents of which are fixed and can be read again and again, an oral presentation is ephemeral. Therefore, the standard of proof for ascertaining the contents of an oral disclosure is high. What has been said, or to use the terms of Art. 54(2) EPC, what has been "made available to the public" has to be put beyond reasonable doubt. The board noted that in case T 1212/97 the board had expressed the view that "written notes made at the lecture by at least two members of the audience can usually be regarded as sufficient" for that purpose. A fact also indicated by the board was that the amount of evidence necessary to establish the content of an oral presentation beyond reasonable doubt was to be judged on a case-by-case basis, i.e. it depends on the quality of the evidence in each case. In the current board's view, decision T 1212/97 could not be interpreted as setting an absolute standard for the amount of evidence necessary to prove the contents of an oral disclosure. The board considered that there may be circumstances where evidence from the lecturer and only one member of the audience is convincing enough to reach the standard of proof – i.e. beyond reasonable doubt. In the case at issue, however, evidence from the lecturer and a member of the audience, provided by them in the form of both affidavits and oral testimony, was not considered by the board to prove beyond reasonable doubt that the subject-matter of the claim was disclosed during the lecture. (Both T 1212/97 and T 2003/08 date: 2012-10-31 were cited in T 843/15, in which doubts led the board to conclude that a diagram shown in a conference speaker's slideshow had not been made available to the public).

With respect to oral presentations during a conference, the board in T 667/01 stated that: a declaration of the presenter as to the content of his presentation would not usually be regarded as sufficient since he might have deviated during his presentation from what he intended to present and from what he later remembered as having presented, or he might have presented relevant issues in such a way that the audience was unable to take note of them. If the extent to which the audience understood the presented issues remained uncertain, the established standard of proof typically required a further, independent statement by a person having attended the presentation. Considerable doubt had to remain as to whether the presenter could after 12 years still remember what exactly was presented.