This paper investigates the determinants of Spanish vertical intra-industry trade with a large sample of countries. We empirically test the comparative advantage explanation. For this aim, we build physical, human and technological capital stocks. On average, when using OLS techniques, differences in endowments are a limitation for vertical intra-industry trade. Using quantile regressions techniques, we observe that this negative effect decreases in absolute terms asvertical intra-industry trade flows increase and, in some cases, become positive for the upper tails, thus supporting the view of a reduced version of the comparative advantage explanation.

Keywords: Intra-industry trade, Comparative Advantage, Vertical Differentiation, Capital Stocks, Quantile Regressions.

JEL classification: F11, F12, F14, C23, C24.