The U.S. emitted ~1.58 Pg of fossil fuel carbon in 2001, approximately one quarter of global CO2 production. With climate change increasingly likely, strategies to reduce carbon emissions and stabilize climate are needed, including greater energy efficiency, renewable energy sources, geoengineering, decarbonization and geological and biological sequestration. Two of the most commonly proposed biological strategies are restoring organic carbon in agricultural soils and using plantations to sequester carbon in soils and wood. Here we compare scenarios of land-based sequestration to emissions reductions arising from increased fuel efficiency in transportation, targeting ways to reduce net U.S. emissions by 10% (~0.16 Pg C yr-1). Based on mean sequestration rates, converting all U.S. croplands to no-till agriculture or retiring them completely could sequester ~0.059 Pg C yr-1 for several decades. Summary data across a range of plantations reveal an average rate of carbon storage an order of magnitude larger than in agricultural soils; in consequence, one-third of U.S. croplands or 44 million ha would be needed for plantations to reach the target of ~0.16 Pg C yr-1. For fossil fuel reductions, cars and light trucks generated ~0.31 Pg C in U.S. emissions in 2001. To reduce net emissions by 0.16 Pg C yr-1, a doubling of fuel efficiency for cars and light trucks is needed, a change feasible with current technology. Issues of permanence, leakage, and economic potentials are briefly discussed briefly, as is the recognition that such scenarios are only a first step in addressing total U.S. emissions.