Stakeholders throughout the United States are currently working to reach a consensus on the structure and protocols that will define tradable transmission rights in the context of the various wholesale electricity markets, and their associated Independent System Operators (ISOs), now forming in different regions of the U.S.  Much of the discussion has focused on the relative merits of physical transmission rights in comparison with financial transmission rights.   To the extent that transmission rights provide their owners with an added level of influence or control over transmission markets, some of the historical industry concerns over vertical market power may need to be revisited.   In this paper, I discuss some of the potential concerns over transmission rights and their use for the exercise of various forms of market power.