177According to the contested decision, the only horizontal effect of the concentration on all the electricity markets lies in the disappearance of GDP as the most likely important potential competitor of EDP. As regards, first, the wholesale electricity market, the Commission has set out a number of factors which demonstrate, on a general level, that it is economically rational and profitable for a gas supplier to enter the wholesale electricity market (recitals 335 to 344). That general incentive is confirmed by the market test and by the example of other Member States in which the liberalisation of those markets has led to such a result, particularly in Spain and the United Kingdom. Furthermore, the Commission provided, during the procedure before the Court, the grounds which for reasons of confidentiality are not disclosed in the contested decision and which demonstrate GDP's individual interest in entering the electricity generation market (recitals 345 to 361). As regards, second, the emergent market or markets for balancing power and ancillary services, the Commission considers that the disappearance of GDP as a potential entrant into the wholesale market also means the disappearance of a significant potential entrant into the markets concerned, whereas the entry of GDP into the wholesale market would weaken EDP's position on those markets (recitals 430 to 432). As regards, third, the retail electricity markets, the Commission considers that GDP was the significant potential competitor owing to its existing commercial presence, the renown of its national trade mark and its capacity to make dual supplies (electricity + gas). The Commission relied in that regard largely on the market test and on examples taken from the situation in other Member States (recitals 449 to 473).