The Internet technology reduces the cost of transmitting and exchanging information. ECNs exploit this opportunity to compete with incumbant stock exchanges. They enable all investors to place quotes, at very little cost.\ Does this lead to competitive liquidity supply? We analyze empirically trades and order book dynamics using the Nastraq dataset and data downloaded from the Island website. The Nasdaq touch is frequently undercut by Island limit orders, using the finer tick size prevailing on that ECN. Liquidity supply on Island is not perfectly competitive, however. On average Island limit orders earn rents.