The growing commodity market for corn ethanol will likely reduce direct greenhouse gas (GHG) emissions associated with fossil fuel combustion in the US, but projected increases in cropland to accommodate this bioenergy commodity will also impact GHG emissions from soils. In the recent past, US agricultural soils have been a net sink for atmospheric CO₂, largely due to enrollment of land in Conservation Reserve Program (CRP). Conversion of formerly enrolled lands into corn production seems likely with about 40% of contracts ending during the next 5 years. Corn production is also likely to increase on lands currently used for other crops or crops grown in rotation with corn, such as soybeans. Conversion of former CRP lands will lead to a release of CO₂ that had been sequestered in soils during recent decades, although losses may be reduced with no-till management. In contrast, increasing corn production on existing croplands is likely to enhance soil C sequestration due to the high residue amounts from corn. Soil N₂O emissions will also be influenced by land management decisions. High fertilization rates are common in corn production and this will increase soil N₂O emissions on former CRP lands and existing croplands supporting bioenergy commodities. However, fertilizer application during periods of high growth and use of nitrification inhibitors would limit these emissions. It is likely that soil-associated emissions will reduce some of the benefit of corn ethanol production for mitigation of GHG emissions, but the net effect will depend on land management decisions.