In accordance with the case law of the boards of appeal, a course of action can be considered obvious within the meaning of Art. 56 EPC if the skilled person would have carried it out in expectation of some improvement or advantage (T 2/83, OJ 1984, 265). In other words, obviousness is not only at hand when the results are clearly predictable but also when there is a reasonable expectation of success (T 149/93). It is not necessary to establish that the success of an envisaged solution of a technical problem was predictable with certainty. In order to render a solution obvious it is sufficient to establish that the skilled person would have followed the teaching of the prior art with a reasonable expectation of success (T 249/88, T 1053/93, T 318/02, T 1877/08, T 2168/11, T 867/13).

In some decisions, especially in the field of biotechnology, the boards have asked whether in the cases in point it was obvious for the skilled person to try a suggested approach, route or method with a reasonable expectation of success (T 60/89, OJ 1992, 268). For more about biotechnological inventions and the definition of the skilled person, see also point I.D.8.1.3 below.

In T 2168/11 the board referred to the case law, according to which the expectation of success depended on the complexity of the technical problem to be solved. While for very ambitious problems requiring the consideration of all the features relied on by the respondent (patent proprietor) but not contained in claim 1, important difficulties might be expected a priori, less ambitious problems might normally be associated with higher expectation of success (see T 192/06, T 782/07).

In line with T 918/01, the board in T 1577/11 concluded that, given the superior efficacy of anastrozole, as compared with tamoxifen, in treating advanced breast cancer, there was a reasonable expectation it would also improve the treatment of early breast cancer, as compared with that achieved with tamoxifen.

In T 296/93 the board held that, in relation to inventive step, the fact that other persons or teams were working contemporaneously on the same project might suggest that it was "obvious to try" or that it was an interesting area to explore, but it did not necessarily imply that there was a "reasonable expectation of success". A reasonable expectation of success should not be confused with the understandable "hope to succeed"; it implied the ability of the skilled person to predict rationally, on the basis of the knowledge existing before a research project was started, the successful conclusion of the said project within acceptable time limits. The more unexplored a technical field of research was, the more difficult it was to make predictions about its successful conclusion and, consequently, the lower the expectation of success (T 694/92, OJ 1997, 408). According to T 207/94 (OJ 1999, 273), the "hope to succeed" was merely the expression of a wish, whereas a "reasonable expectation of success" presupposed scientific appraisal of available facts.

In T 187/93 it was stated that even if it was obvious for the skilled person to try an experiment, it was not necessarily true that this person would have any reasonable expectation of success when embarking on it.

In T 223/92 the board said that in 1981, given the state of the art at that time, the skilled person would have opted for DNA-recombination technology only if relying, e.g., on his own good luck and inventiveness to overcome the known (and as yet unknown) problems involved, which would have caused the average skilled person to expect to fail.

In T 923/92 (OJ 1996, 564) the board had to decide whether the skilled person would have attempted, with reasonable expectation of success, to produce cDNA coding for human t-PA, or whether in this instance he would have known from his technical knowledge, before even embarking on the research, that he would be able to complete his project within an acceptable time. The board bore in mind that, as stated in T 816/90, even when it is possible to theoretically conceive a straightforward approach to solve a specific technical problem, the skilled person might be confronted with unexpected difficulties when trying to put the conceived strategy into practice. The board stated that, although hoping to succeed, the skilled person embarking on this project would have known that its successful conclusion depended not only on technical skill in putting into practice the sequence of precise steps of the theoretical experimental protocol, but to a large extent also on the ability to take the right decisions along the way whenever a difficult experimental situation so required. Under these circumstances, it could not be said that the skilled person had a reasonable expectation of success.

In T 386/94 (OJ 1996, 658), again citing T 816/90, the board ruled that, in gene technology, inventive step could not be acknowledged if, at the priority date, a skilled person could expect to perform the cloning and expression of a gene in a fairly straightforward manner, and the cloning, although requiring much work, did not pose such problems as to prove that the expectation of success was ill-founded.

Where the expression of a cloned DNA in a chosen foreign host constituted the subject-matter of the claimed invention, the question whether a reasonable expectation of success existed or not could be evaluated only by taking into account real difficulties relating to that step. Thus, in order to be considered, any allegation that features jeopardised a reasonable expectation of success had to be based on technical facts (T 207/94, OJ 1999, 273).

In T 737/96 the board was of the opinion that it was not appropriate to attempt to evaluate the expectation of success of a random technique such as mutagenesis where results depended on chance events. This was because the skilled person knew that, unless a specific selection method could be developed, which was not the case in the patent in suit, perseverance and chance played a key role in achieving success, as no form of control could be exerted over the mutation events. Under these circumstances, as in a lottery game, the expectation of success always ranged irrationally from nil to high, so it could not be evaluated in a rational manner based on technical facts (see also T 694/92, OJ 1997, 408).