We examine execution costs for trades in NYSE issues completed on the NYSE, the NASD dealer market, and the regional stock exchanges during 1994. We find that effective bid-ask spreads are only slightly smaller at the NYSE. However, realized bid-ask spreads, which measure market-making revenue net of losses to betterinformed traders but gross of inventory or order-processing costs, are lower on the NYSE by a factor of two to three. This differential is attributable to the successful ‘cream skimming’ of uninformed trades by off-NYSE market makers. These findings reinforce existing concerns about whether orders are routed so as to receive the best possible execution.