Since the beginning of the nineties, professional sports firm values have been estimated by American newspapers. In 2004, Forbes proposed for the first time a list of the most valuable European soccer teams. In this article, we compare the determinants of firm values in MLB, the NBA, NFL, NHL, and European soccer over the period 2004-2011. The results show only one variable for which the sign and significance are the same for all the leagues: historical sports performance, with a significantly positive impact in each league. The comparison between the United States and Europe reveals that a majority of differences seem to indicate that the determinants of team values in the United States are not the same as those in Europe. Lastly, we proposed avenues for future research: integrating an international dimension that could be measured through the number of fans on social media and player values.