We show that very large firms shape country export patterns. Among 32 countries, the top firm on average accounts for 14 percent of a country's total (non-oil) exports, and the top 5 firms make up 30 percent. These export superstars are also important in the sectoral distribution of exports. Variation in exports from the top firm in a country explains about one third of the variation in sectoral exports relative to income across countries and variation in exports from the top 5 firms explains nearly half. Revealed comparative advantage in a sector can be created by a single firm. JEL codes: D22, F14 511 using the Balassa index and the regression-based method proposed by Costinot, Donaldson and Komunjer (2012). We then calculate the share of industries that would lose RCA in the absence of the superstars, according to each measure. Both the Balassa and Costinot et al. methods suggest that in about one fifth of the countries, the top firm creates a revealed comparative advantage that otherwise would not exist;511

Using a novel dataset with transaction-level level exports from Malawi, Mali, Senegal and Tanzania, we explore the determinants of the survival of firm-product-destination combinations past the first year after entry on export markets. We find that survival correlates with diversification (or experience) at the extensive margin: a firm-productdestination combination is more likely to survive if the firm ships more * This paper is part of a World Bank research project initiated by Paul Brenton and Denisse Pierola. Financial support from the BNPP Trust Fund on Improving the Survival of African Exports is gratefully acknowledged. We are also grateful to the Malawi Revenue Authority, the Direction Générale des Douanes du Mali, the Direction Générale des Douanes du Sénégal, and the Tanzania Revenue Authority for their cooperation and willingness to share data. We also thank Frances Aidoo, William Baah-Boateng, Sidiki Guindo, Anthony Mveyange and Nelson Nsiku for their assistance in the collection of the customs data used in this paper. products to that destination, or if it ships that product to more destinations, suggesting synergies within the firm. Most strikingly, we find significant evidence of cross-firm synergies: a firm-product-destination is more likely to survive, the more firms from the same country export the same product to the same destination. These results may suggest a case for export promotion at the national level.

a b s t r a c tHow can developing countries stimulate and sustain strong export growth? To answer this question, we examine 92 episodes of export surges, defined as significant increases in manufacturing export growth that are sustained for at least 7 years. We find that export surges in developing countries tend to be preceded by a large real depreciation, which leaves the exchange rate significantly undervalued. In contrast, in developed countries, the role of the exchange rate is less pronounced. We examine why the exchange rate is important in developing countries and find that the depreciation is associated with a significant reallocation of resources in the export sector. In particular, depreciation stimulates entry into new export products and new markets. These new exports are important, accounting for over 40% of export growth on average during the surge in developing countries. We argue that a large real depreciation induces firms to expand the product and market space for exports.

The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

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