In T 570/08 the opponents had filed evidence in the form of comparative tests with the aim to support their argument that the claimed additive composition in the patent-in-suit did not solve the problem of improving lubricity and solubility of a diesel fuel oil. These results were in contrast to the tests which the patent proprietor had provided, so that the board was confronted with a series of tests leading to contradictory results. Therefore the board could not share the patent proprietor's argument that the burden of proof rested with the opponents, since the opponents' test results cast doubts on the effect allegedly achieved by the present invention. The patent proprietor could not convincingly eliminate those doubts and the patent was revoked.

In T 473/13 the board considered the arguments and the supporting evidence (an affidavit by the project manager and inventor of the patent in suit) submitted by the respondent (patent proprietor) to be sufficient to discharge its initial burden of proving that there had been a confidentiality agreement. The burden of proof then shifted to the intervener, which had to establish that there had been no such confidentiality agreement. The intervener had, however, presented no arguments or evidence which objectively might cast doubt on the existence of a confidentiality agreement, but had merely presented speculation in this respect. The intervener did not try to contact the utility company V, with which the patent proprietor had a co-operation, to enquire of them whether they considered a confidentiality agreement to have been in place. The intervener also did not make enquiries of other organisations active in the technical field in order to address the question whether such confidentiality agreements represented normal practice. The board concluded that the public nature of the prior use was not proven, such that it did not form part of the prior art.

In T 131/03 the board pointed out that, once the opponent had established a strong presumption that unusual parameters as those used to define the claimed subject-matter were inherently disclosed in the prior art, the patent proprietor could not merely claim the benefit of the doubt. It was incumbent upon the patentee to establish the extent to which the parameters used in the definition of its invention actually distinguished the claimed subject-matter from the prior art. See also T 1452/16 (unusual parameters – alleged prior use – public availability of a product): as to the possibility for the patent proprietor to obtain samples and test them, the board stated that when testing samples manufactured after the priority date the legitimate question could arise of whether the results obtained were representative of the ratios present in the samples of the prior art. However, by using a parameter which had not been used in the prior art, the burden was on the patentee to prove that the prior art did not fall within the terms of the claim.

The burden of establishing insufficiency of disclosure generally lies with the opponent. When the patent does not give any information on how a feature of the invention can be put into practice, only a weak presumption exists that the invention is sufficiently disclosed. In such case, the opponent can discharge the burden of proof by plausibly arguing that common general knowledge would not enable the skilled person to put this feature into practice. The patent proprietor then bears the burden of establishing the contrary assertion that common general knowledge would indeed enable the skilled person to carry out the invention (T 63/06, summary of this case law in T 347/15). In T 338/10, citing this approach, the board held that the reasoned arguments submitted by the respondent (opponent) reversed the burden of proof, placing the onus on the appellant to show that the skilled person would have considered it likely that the claimed therapeutic effect was obtainable in the case in point, despite a lack of data and thus only a weak presumption. But since the appellant had not responded by submitting any arguments or evidence, the board held that the patent as granted did not comply with Art. 83 EPC (the principles applicable in the context of that article are recalled for example in T 518/10, see chapter II.C.9.).

In T 1846/10 the board observed that example 5 of the patent provided verifiable facts which raised serious doubts that the invention could in fact be carried out by the average person skilled in the art without undue experimentation or inventive skills by following the guidance provided in the patent. Under these circumstances, no additional experimental evidence from the appellant (opponent) was required as it could rely on the evidence provided by the patent itself. The board concluded that the appellant had discharged its burden of proof.

In T 2070/13, as to the burden of proof, serious doubts were set out concerning whether the skilled person's common general knowledge would be sufficient to enable him to carry out the invention. As a consequence, the burden of proof shifted to the patentee. The mere assumption that anti-adherence of the claimed groups of compounds was known, and the reference to post-published D16 referring to a particular bacterial non-adhesion, was not convincing evidence that could discharge the respondent (patentee) from its burden of proof.

In T 792/00 the board found that if the patent contained only an example with a hypothetical experimental protocol, and if this example was to be relied on for showing sufficiency, then the burden of proving that this protocol worked in practice as stated lay with the patentee. Evidence that a variation of the protocol worked was unlikely to be enough. However, if the example contained a complete experimental protocol and the patentee affirmed that the results reported had been obtained, a board was likely to accept that the patentee had done enough to shift the burden of proof to the opponent who would then have to provide a repeat of the experiment in order to convincingly demonstrate that the protocol did not, in fact, work as stated.

In T 967/09 the board was satisfied that opponent III had substantiated, by means of verifiable facts, serious doubts that the patent did not disclose the invention as defined in claim 1 in a manner sufficiently clear and complete for it to be carried out by the skilled person. These doubts were considered not to be convincingly rebutted by the appellant (patent proprietor). Accordingly, the board considered that respondent (opponent III) had discharged its burden of proof in this respect. Therefore the patent, in respect of the subject-matter of claim 1, was insufficiently disclosed. T 1842/06 sets out various evidential requirements under Art. 83 EPC, especially those applicable in ex parte proceedings. It states that if an examining division or board objects that the description's disclosure is insufficient, it bears the burden of proving that. If an invention is "revolutionary" (e.g. linked to the "memory of water"), reversing this burden of proof may be justified if the claimed invention's feasibility and reproducibility does not appear sufficiently plausible on the basis of the application. Doubts might arise for example merely because a technical effect that is a priori contrary to the laws of physics is not adequately substantiated by experimental results.

In T 518/10 the appellant (patent proprietor) argued that the burden of proof that an extract comprising compound (II) could be obtained from aquatic or marine biomass, in particular krill, did not shift to the appellant. The patent in suit provided at least one way as to how such an extract could be obtained. Furthermore, the extraction of compound (II) from krill was not against the laws of physics as argued by the respondents (opponents). The board was not convinced and stated that in the present case, assertion of the appellant was against the prevailing technical opinion. The respondents provided evidence that compound (II) could not be obtained when working according to the general method described in the patent. By their experimental reports, the respondents conclusively showed that, by following the extraction method described in the patent in suit, it was not possible for the skilled person to obtain the claimed extract comprising compound (II). Since this fact was neither disproved by documents filed by the appellant nor refuted by the appellant's counter-arguments, the board concluded that the ground of Art. 100(b) EPC was made out.

In R 21/10 the Enlarged Board ruled that a board's alleged reversal of the burden of proof is not a ground for review, these being exhaustively listed in Art. 112a(2)(a) EPC to Art. 112a(2)(e) EPC and R. 104 and 105 EPC. It found that, in any event, the technical board concerned – far from reversing the burden of proof – had merely applied the rule that each party bears the burden of proving the facts it asserts.