An applicant may pay additional search fees in the international phase if invited to do so by the ISA under Art. 17(3)(a) PCT.
Once the application has entered the European phase, R. 164 EPC "Unity of invention and further searches" (rule amended by Decision of the Administrative Council dated 16 October 2013, OJ 2013, 503) allows applicants to obtain, upon payment of a (further) search fee, a seach of any invention claimed which was not searched by the EPO in the international phase. Moreover, applicants may choose any invention searched by the EPO either in the international phase, in the procedure for supplementary search or in the procedure under amended R. 164 EPC as a basis for further prosecution of the European phase (see Notice of 10 June 2014, OJ 2014, A70). Amended R. 164 EPC entered into force on 1.11.2014. For the transitional regime see Notice (supra), IV.23. and 24.