Over the past 20 years a steadily increasing number of researchers have investigated the relationship between neighbourhood demographic composition and environmental hazard presence. However, relatively few researchers have attempted to determine why the distribution of social groups around environmental hazards takes the form that it does or why some studies find strong evidence of environmental racial inequality while others do not. One possible explanation for this is that environmental racial inequality levels vary from one location to another. In order to see if this is the case, the article compares environmental racial inequality levels in the 61 largest metropolitan areas in the continental US, holding the unit of analysis, type of hazard, type of region and comparison population constant across metropolitan areas. Analyses demonstrate that environmental racial inequality levels do vary across metropolitan areas. Thus, after presenting these analyses, hypotheses are tested that make predictions about the determinants of this variation. These hypothesis tests show that neither residential segregation nor racial income inequality does a good job of explaining metropolitan-area variation in environmental inequality outcomes in the US.