Forbes Magazine estimates of annual revenues, costs and team values for professional sports teams are used to derive market power measures for teams in four major professional sports leagues: the MLB, NBA, NHL, and the NFL. Two variants of the Lerner Index, one that reflects short-term operations for the past year and another reflecting the long-run net present value of the franchise are derived over the 2006-2016 period. Only the long-run measure provides estimates that are always consistent with theoretical requirements. Analysis of variance of long-run market power shows that local market factors and past team performance have less impact on market power than common league-wide effects. Team market power depends least on local team effects in leagues that have stronger revenue sharing policies. Price-cost margins are higher for professional teams in North American than for the most valuable European soccer teams, consistent with the stronger exemption from anti-trust law in the U.S.