For the forthcoming Supplemental Poverty Measure (SPM), the U.S. Census Bureau will use the method proposed by the 1995 National Academy of Sciences (NAS) Panel on Poverty and Family Assistance – subtracting a flat amount from a family’s resources for ‘other’ work-related expenses, with an annual inflation adjustment (see Short 2001). This research examines the appropriateness of applying a flat amount for work-related expenses by investigating geographic variation in average commuting expenses for automobile commuters across 100 urban areas, regions, and divisions, as defined by the U.S. Census Bureau, using two methods: (1) state gas prices and (2) federal reimbursement rate. This research found that these two methods produce significantly different cost estimates. Cost estimates also vary by population size, region, and division. Overall, this research found that there is significant geographic variation in commuting costs and recommends the SPM be adjusted accordingly.