Although there is a general consensus that the market is unified, here we quantify the factors that create regions by analyzing the price relation between 33 crude oils. ADF statistics indicate that 447 of the 528 crude oil pairings cointegrate; 81 do not. The presence/absence of cointegration is analyzed using a logit model. The likelihood that the prices for two crude oils cointegrate depends on their physical characteristics (density and sulfur content), economic factors (country risk for the nation of origin), their geographic location (distance between supply ports), and political factors (OPEC membership). Over the sample period, the technology to refine heavy crude oils penetrates the market, and this reduces the price difference between heavy and light crude oils. The effect of country risk implies that crude oils from high risk nations are not perfect substitutes for crude oils of similar quality from low risk nations. Finally, crude oils from widely separated suppliers are more likely to cointegrate than crude oils from near-by nations, which suggests consumers diversify supply across transportation chokepoints. For this sample, these sources of regionalization add $0.20 per barrel to the $2.86 average price difference between crude oils in the same market. Together, these factors have important implications for the efficacy of policy aimed at reducing dependence on unreliable suppliers and the spill-over effects of holding inventories. (C) 2014 Elsevier Ltd. All rights reserved.