This article examines the trade in wild rubber that emerged in Upper Guinée, in the colony of Guinée Française, at the end of the nineteenth century. Guinée's rubber boom went through two phases. The first, from the 1880s to 1901, was dominated by local collectors and Muslim traders who directed the trade to the British port of Freetown, Sierra Leone. In the second phase, 1901–13, expatriate merchant houses entered the long-distance trade and, with the help of the colonial state, reoriented the commerce to Conakry, port city and capital of Guinée. The Guinée case offers an alternative perspective to that provided by the better studied rubber markets of Central Africa and South America, and contributes to scholarly debates about export economies, colonial rule and social change. In Guinée, local production and commercial networks maintained significant influence in the market throughout the rubber boom, thwarting colonial efforts to control the trade. The colonial state proved particularly challenged by the practice of rubber adulteration, whereby local collectors and traders corrupted rubber with foreign objects to increase its weight. While the trade exposes the limits of colonial power, rubber also played a largely overlooked role in the social and economic transformations of the period. Evidence suggests that profits from the rubber trade enabled peasants, escaped slaves and former masters to alter their circumstances, accumulate wealth and rebuild homes and communities destroyed during the preceding era of warfare and upheaval.