This paper documents the evolution of variables central to understanding the creation of an Atlantic Economy in wheat between the US and the UK in the nineteenth century. The cointegrated VAR model is then applied to the period 1838-1913 in order to find long-run relationships between these variables. The main result is that explanations for the expansion of trade based on falling barriers to trade need to be augmented by another factor: the expansion of US supply. This implies that the growth of the Atlantic Economy cannot wholly be attributed to the decline in transportation costs, as is usually considered to be the case