The objection of lack of sufficient disclosure presupposes that there are serious doubts, substantiated by verifiable facts (T 19/90, OJ 1990, 476; T 890/02, OJ 2005, 497). Otherwise it is unlikely to succeed (T 394/06, T 1437/07). There is no requirement for an example in the patent (T 1437/07).
In order to establish insufficiency, the burden of proof is upon an opponent to establish on the balance of probabilities that a skilled reader of the patent, using his common general knowledge, would be unable to carry out the invention (T 182/89, OJ 1991, 391). A mere statement that one of several examples in a patent has been repeated once "exactly as described" without obtaining exactly the results claimed in the patent is in principle inadequate to discharge that burden (see also T 406/91, T 418/91, T 548/91, T 588/93, T 465/97, T 998/97, T 499/00 and T 751/00). Where the parties make contradictory but unsubstantiated assertions concerning facts relevant for establishing patentability and the EPO is not in a position to establish the facts of its own motion, the benefit of the doubt is given to the patent proprietor (T 72/04). If the patent contains only an example with a hypothetical experimental protocol, and this example is to be relied on for showing sufficiency, then the burden of proof lies on the patentee to show that in practice this protocol works as stated. Evidence that a variation of this protocol works is unlikely to be enough (T 792/00). For more details see chapter III.G "Law of evidence"). However, the patent at issue in T 397/02 disclosed a specific humanized version of a mouse antibody and also many specific alternatives thereof. The case was therefore not comparable to T 792/00 (or T 984/00) where not a single specific example of the claimed subject-matter was disclosed. Thus the appellant-opponent bore the burden of proving that the invention could not be carried out.
The board in T 63/06 agreed that the burden of proof generally lies upon an opponent to establish insufficiency of disclosure. When the patent does not give any information as to how a feature of the invention can be put into practice, only a weak presumption exists that the invention is sufficiently disclosed. In such a case, the opponent can discharge his burden by plausibly arguing that common general knowledge would not enable the skilled person to put this feature into practice. The patent proprietor then has the burden of proof for contrary assertion that common general knowledge would indeed enable the skilled person to carry out the invention. In T 491/08 the board, referring to T 63/06 held that a presumption exists that, in general, a patent application relates to an invention which is disclosed in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art. The weight of arguments and evidence required to rebut this presumption depends on its strength. A strong presumption requires more substantial arguments and evidence than a weak one. If a patent application does not contain detailed information of how to put the invention into practice, this requires less substantial arguments and evidence. Serious doubts whether the skilled person can carry out the invention as claimed, e.g. in the form of comprehensible and plausible arguments, are sufficient.
As proof that an invention has been insufficiently disclosed, the boards require that the attempt to repeat it must fail despite following the conditions given in the examples. This requirement is not fulfilled where the opponent repeats the patented process under conditions covered by claim 1 but differing in many respects from those applying in the contested patent's examples (T 665/90).
An invention should be reproduced using the examples given. Insufficiency cannot be proven on the basis of laboratory trials when the only embodiment exemplified in the patent is an industrial fermentation process (T 740/90). The disclosure was also considered sufficient where the opponent had only used equivalents of the surfactants given in the patent, as he had not discharged his burden of proof (T 406/91).
It was held in T 541/96 that if an invention seems to offend against the generally accepted laws of physics and established theories, the disclosure should be detailed enough to prove to a skilled person conversant with mainstream science and technology that the invention is indeed feasible, the onus being on the applicant (see also T 1023/00, T 1329/07 and T 1796/07). The more a new invention contradicts previously accepted technical wisdom, the greater the amount of technical information and explanation is required in the application to enable the invention to be carried out by the average skilled person to whom only that conventional knowledge is available (T 1785/06).