ACER published its opinions on proposed projects of common interest (PCI) for trans-European networks for electricity and gas in 2013. While taking into account the difficulties encountered during the preparation of the draft regional lists of PCIs and some methodological weaknesses of the process, the Agency believes that the draft regional lists of gas, electricity transmission and electricity smart grids projects merit adoption as the first Union list of PCIs. The Agency suggests complementing the 2013 Union list by additional information about the degree of maturity, costs and benefits of each individual PCI, and believes that the complementary information could be added soon after 31 October 2013 -deadline for the submission of investment requests by project promoters. The Agency also notes that all PCIs will be fully reassessed in the next PCI selection round, in line with the Regulation 347/2013 and that the assessments should follow the detailed recommendations provided in the two Agency opinions. Such recommendations include, among others: the set-up of a proper data base needed for the consistent assessment of the projects; the continuation of work by ENTSOs to further improve the Ten Year Network Development Plans for use in PCI selection; the improvement of data collection by using revised questionnaires for project promoters; the application of a consistent clustering approach throughout Europe; and the timely development of sound cost-benefit analysis methodologies that would include the monetisation of costs and benefits.