In this paper we simulate the impact of removing all tariffs on imports under both competitive and Cournot oligopoly market structures with and without barriers to entry and exit. We find that trade liberalization induces welfare gains equal to 1 percent with perfect competition and 0.9 percent with increasing returns to scale, oligopoly and barriers to entry and exit, but welfare losses equal to 0.4 percent with free entry and exit. Sensitivity analysis shows that welfare losses depend on elasticities of substitution between imported and domestic goods and cost disadvantage ratios.