Activities to reduce net greenhouse gas (GHG) emissions by biological soil or forest carbon sequestration utilize currently known and readily deployable technologies. Many other GHG emission reduction options require future technological development or must wait for turnover of capital stock. This paper reports on methods to simulate terrestrial carbon sequestration activities using a sequence of three models: a biophysical crop growth model, an economic model of U.S. agriculture, and an economy-wide economic model for the U.S. to place terrestrial mitigation options in context with other options to reduce net greenhouse gas emissions. Although our methodology should be broadly applicable to a variety of terrestrial mitigation options, we select agricultural tillage practices as an example to demonstrate our approach. Our analysis addresses the following questions: How significant a contribution could agriculture and forestry make relative to non-agricultural (e.g., energy and industrial) mitigation possibilities? What analysis tools can help us estimate terrestrial mitigation potential and how robust are these estimates?