Using a newly constructed dataset on the quantities and prices of African commodities over the long 18th century this paper provides new insights into the changing nature of the non-slave trade with West Africa in the era before the abolition of the British transatlantic slave trade. We find that previous estimates of both the volume and value of the commodity trade have been underestimates and fail to account for regional variations in output. Our data shows that from the 1770s there was a significant expansion in what would later be called ‘legitimate commerce’. This growth was centred around the Bight of Biafra and that the vast majority of these goods were purchased by slave ships, not the specialist bi-lateral traders who had dominated the trade earlier in the century. We argue that slave merchants were motivated by both rising prices in European markets and by the relative stability of prices on the African coast. Furthermore, we suggest that both European and African merchants faced increasing levels of risk in the latter decades of the 18th century. This may have prompted some of the them to diversify their portfolios of goods through investment in the commodities trade to better manage these risks.