As in most commodities markets, deregulated electricity markets allow the participation of purely financial traders to enhance informational and productive efficiency. The presence of financial players is expected, among other things, to help eliminate predictable pricing gaps between forward and spot prices, which may arise in the presence of market power and are linked to productive inefficiency. However, we find that the impact of financial players on reducing pricing gaps has been limited, even using credibly exogenous variation in financial activity to address potential endogeneity. A forward premium persists. We show that financial traders effect on the premium was limited by two barriers. First, arbitrageurs do not have unlimited access to capital. Trading was reduced during the financial crisis, when capital availability was restricted. The second is regulation, as high transaction costs imposed by the regulator restricted arbitrage. Moreover, during this period we observe that some financial players appear to be betting in exactly the opposite direction of the pricing gap, sustaining large losses while doing so. We find evidence consistent with participants using forward market bids to affect congestion and thus increase the value of their Financial Transmission Rights (FTR), i.e. these financial players incur losses with one financial instrument to make larger profits with another, introducing artificial congestion to the system.