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 The patent proprietor could not convincingly eliminate those doubts and the patent was revoked.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 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.
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).
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.