This report assesses the formation of wholesale electricity prices in Portugal in the second half of 2007, a period that coincides with the first 6 months of operation of MIBEL. The analysis carried out identified a wide range of factors that may have contributed to the existence of these wholesale price differences in Portugal and in Spain, from issues related to differences in generation costs and unavailability of thermal power plants, to issues related to the supply structure of the two countries. The AdC notes that the entry of new players with combined cycle plants using natural gas can promote competition. In this context, the creation of the MIBEL day-ahead market, as a harmonized price formation mechanism in the Iberian space, is an essential step towards realizing the benefits of the entry of new competitors.