This study investigates the impact of boat engine power on Vietnam fishery output in27 coastal provinces during 2000-06. The study shows that many fisheries are producingsignificantly under capacity. Inefficiencies arise from unregulated uses of small and lesspowerful boats, primarily for inshore and near-shore fishing, which leads to overcrowding,while leaving offshore fisheries largely underexploited. Mismanaged increases in thenumber of small fishing boats of less than 45 horsepower (HP) appear to have an adverseimpact on total catches. More powerful vessels, especially vessels with an engine capacityof at least 150 HP for offshore fishing, are most efficient.