This paper first elaborates a model of intermediate selection where potential migrants must have both the resources to finance the migration cost (liquidity constraint restriction) and an income gain of migrating (economic incentives restriction). We then test the predictions of the model regarding the impact of output in the sending country and migration costs on average skill level of immigrants to the United States from 1899 to 1932, where immigration was initially unrestricted by law and then highly limited. Our panel of 39 countries includes data on occupations that immigrants had in their country of origin, providing a more accurate skill measure than previously available datasets. We find that migration costs have a negative but skill-neutral effect on quantity of immigrants and an increase in output, measured as GDP per capita, has a positive effect on quantity and a negative effect on average skill level of immigrants, suggesting that the main channel by which changes in output affected the average skill level of migrants in that time period is through the easing or tightening of the liquidity constraints and not through the economic incentives as in previous models. Also, using migrants’ occupation in the United States as a measure of skills would lead to misleading conclusions.