According to established case law of the boards of appeal, a successful objection of insufficient disclosure presupposes that there are serious doubts, substantiated by verifiable facts. In inter partes proceedings, the burden of proof initially lies with the opponent, who must establish, on the balance of probabilities, that a skilled person reading the patent, using common general knowledge, would be unable to carry out the invention. If the opponent has discharged its burden of proof and so conclusively established the facts, the patent proprietor then bears the burden of proving the alleged facts.
Indeed, a successful objection of a lack of sufficiency of disclosure presupposes that there are serious doubts, substantiated by verifiable facts (see e.g. decision T 19/90, OJ 1990, 476 and decision T 890/02, OJ 2005, 497). In order to establish insufficiency of disclosure in inter partes proceedings, the burden of proof is upon an opponent to establish, on the balance of probabilities, that a skilled person reading the patent, using his common general knowledge, would be unable to carry out the invention (see decision 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, T 751/00 and T 967/09). 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). However, the patent at issue in T 397/02 disclosed a specific humanised 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.