We investigate the impact of passenger shipping cartels on trans-Atlantic migration during the early twentieth century. We assemble from primary sources a detailed database of passenger flows and cartel operations and show that cartel operation reduced migratory flows by approximately 20% to 25%. Further, we show that there was no strong intertemporal substitution in migration to North America (at least in the short run) and, therefore, that the effects of cartel operation were not “undone” by later migration. Lastly, we find that cartel operation had no appreciable effect on the variability of migration flows, providing evidence against the notion that unfettered competition was destabilizing to turn-of-the-century transportation markets.