This article examines how much of the dispersion in economic performance across OECD countries can be accounted for by the proximity to areas of dense economic activity. To do so, various indicators of distance to markets and transportation costs are added as determinants in an augmented Solow model, which serves as a benchmark. Measures of distance to markets are found to have a statistically significant effect on GDP per capita. And the estimated economic impact is far from negligible. The reduced access to markets relative to the OECD average could contribute negatively to GDP per capita by as much as 11% in Australia and New Zealand. Conversely, a favourable impact of around 6-7% of GDP is found in the case of two centrally-located countries: Belgium and the Netherlands. The paper provides also some tentative evidence that spending on R&D and human capital might have a stronger effect on GDP per capita in countries with a higher degree of urban concentration.