The European search is essentially a thorough, high-quality, all-embracing search. Nevertheless, it must be realised that in a search of this kind, 100% completeness cannot always be obtained, because of such factors as the inevitable imperfections of any information retrieval system and its implementation. The search is carried out in such a manner as to reduce to a minimum the possibility of failing to discover complete anticipations for any claims, or other highly relevant prior art. For less relevant prior art, which often exists with a fair amount of redundancy amongst the documents in the search collection, a lower recall ratio can be accepted (see in this context, however, B‑III, 2.3). For limitations of the subject-matter searched by the EPO, see B‑VIII.

The scope of the international search is defined in Art. 15(4) PCT stipulating that the International Searching Authority must endeavour to discover as much of the relevant prior art as its facilities permit and must, in any case, consult the documentation specified in the PCT Regulations (Rule 34 PCT). It follows from this definition ("as its facilities permit") that the scope of an international search must be equivalent to a European search. International and European searches must thus be fully compatible. In accordance therewith, if the EPO carried out the international search or the supplementary international search, no supplementary European search report need be drawn up and the international search report made by the EPO takes the place of the European search report unconditionally (Art. 153(6) EPC, see OJ EPO 2010, 316, and OJ EPO 2011, 616; see also B‑II, 4.3).