The economic efficiency of cropping options to mitigate net GHG emissions from agriculture in Eastern Canada was analyzed. Data on yield response to tillage (moldboard plow and chisel plow) and six-corn (Zea mays L.)-based rotations were obtained from a 20-year field experiment in Ontario. Budgets were constructed for each cropping system while GHG emissions were accounted for by soil carbon measurements and estimates of nitrous oxide according to IPCC methodology. Complex crop rotations with legumes, such as corn-corn-soybeans (Glycine max. L.)-wheat (Triticum aestivum L.) with red clover (Trifolium pratense L.) underseeded, have higher net returns and substantially lower GHG emissions than continuous corn. Conservation tillage reduces GHG emissions due to lower input use but sequestration levels did not vary significantly between tillage systems. Rotation had a much bigger effect on the mitigation potential of GHG emissions than tillage. However, opportunity costs of more than $90 per Mg CO2 eq indicate the limits to increase the mitigation potential beyond the level of the most profitable cropping system. (c) 2006 Elsevier B.V All rights reserved.