Greenhouse gas mitigation is possible through carbon sequestration in agricultural soils following adoption of conservation practices. The Conservation Reserve Program (CRP), which was enacted in 1986, paid farmers to retire land from cultivation, and led to sequestration of carbon dioxide (CO2) in soils. However, some CO2 that was sequestered through land retirement may have been re-emitted following cultivation of previous grazing lands. Our objective was to evaluate the likelihood that carbon leakage occurred with CRP enrollment based on a spatial pattern analysis. We examined the relationship between cropland enrollment in the CRP and conversion of grasslands to cultivated cropland, using regional correlations and spatial cross-correlations. Since it is common practice to regularly rotate cultivated cropland and pasture, we reduced our estimates of newly converted cropland by the amount of land placed into pastures before evaluating the potential for leakage. Even with this modification, significant positive correlations between CRP enrollment and cultivation of former grazing lands were found in several Major Land Resource Areas (MLRA) of Montana and South Dakota. These coefficients ranged from 0.40 to 1. We also found that there were positive spatial cross-correlations among counties in these regions, as well as in western Colorado. We estimated approximately 20-30 percent leakage from MLRAs in Colorado and Montana and as much as 100 percent leakage in parts of South Dakota. CRP enrollment within these MLRAs ranged from about 80,000 hectares to over 1,000,000 hectares. While we conclude that there is high potential for CRP leakage in these regions, further studies will be needed to determine that cropland conversion was stimulated by participation in the CRP.