Reversing a High Court decision on the invalidity of two patents, in Schlumberger Holdings Ltd v Electromagnetic Geoservices AS [2010] EWCA Civ 819, Lord Justice Jacob has held that the person skilled in the art can differ, depending on whether the test is used to determine obviousness or in relation to sufficiency and claim interpretation.


Seismic techniques are used in oil and gas (hydrocarbon) exploration to identify layers in sedimentary rock that might contain hydrocarbon deposits. Prior to the invention of the patent for under-sea exploration, the only way to find out whether hydrocarbon was present in an identified layer was to drill an exploration well, costing around US$25m and with a success rate of one in 10.

Controlled Source Electromagnetic (CSEM) surveying is a powerful geophysical tool for mapping electrical resistivity in geological structures beneath the sea floor. The patent, owned by Electromagnetic Geoservices (EMGS), described the use of CSEM on a previously identified (e.g. by seismic methods) layer to find out whether it contained hydrocarbon. Schlumberger claimed that the patent was invalid on grounds of obviousness and lack of novelty. At first instance, Mann J held that the patent was invalid on the ground of obviousness. EMGS appealed this decision to the Court of Appeal.


Jacob LJ, giving the leading judgment of the Court of Appeal, first set about determining the person skilled in the art. He held that the kind of scientist who would be engaged actively by oil and gas exploration companies to find hydrocarbon reserves would be an exploration geophysicist. Such an individual would understand the use of seismics. An exploration geophysicist would have a vague knowledge of CSEM but would have no apparent use for it. An exploration geophysicist could not perform the method of the patent, as one would need the skills of a CSEM expert. Also, to determine the scope of the claims, it was common ground that you would consider them through the eyes of a notional team including both exploration and CSEM geophysicists.

The “person skilled in the art” is referred to in the European Patent Convention in Articles 69, 83 and 56. Articles 69 and 83 are concerned with the position post-grant of the patent; Article 56 refers to the person skilled in the art pre-grant. Jacob LJ rejected Schlumberger’s contention that the same phrase could not have different meanings and stated the flaw was to assume that “the art” was necessarily the same both before and after the invention is made. The assumption may be correct in most cases, but some inventions are themselves artchanging. If a patentee says “marry the skills of two different arts to solve a problem,” marrying may be obvious or it may not. If it is not, and doing so results in a real technical advance, then the patentee deserves and ought to have, a patent. His vision is out of the ordinary.

Jacob LJ held that this was not to say that a different construction was being given to the phrase “person skilled in the art” in the different Articles. It was because the phrase was being applied to different situations. As Jacob LJ explained, where the issue is claim construction or sufficiency, one is considering a post-patent situation where the person skilled in the art has the patent in hand to tell him how to perform the invention and what the monopoly claimed is. But ex-hypothesi, the person skilled in the art does not have the patent when considering obviousness and “the art” may be different if the invention of the patent itself is art-changing.

Jacob LJ held that, in this case, the issue should be approached in two ways. First, would it have occurred to the notional exploration geophysicist that using CSEM would solve the problem? Second, would the notional CSEM expert know of the exploration geophysicists’ problem and, if so, would the CSEM expert appreciate that CSEM had a real prospect of being useful to solve the problem? On the evidence, Jacob LJ concluded that the answer to both questions was in the negative.

Citing Haberman v Jackel [1999] FSR 683, Jacob LJ noted that …there was no real explanation of why the idea was not taken up well before the date of the patent. The simplest explanation—indeed the only one that fits the known facts—is that the inventors hit upon something which others had missed. After finding that none of the cited prior art invalidated the patent, the appeal was allowed.