This paper addresses the assessment of greenhouse gas emissions from agriculture in the European Union. We first estimate and compare net emissions from agricultural activities in twelve EU countries. These estimates are based on a set of farm-unit linear-programming models. We then use these models to derive marginal and total abatement costs associated with different levels of reduction targets (dual approach) and different values of carbon-equivalent emissions (primal approach). Finally, we explore the possibility of allowing afforestation on set-aside land. This paper highlights the discrepancies between countries regarding abatement costs and their sensitiveness to the accounting for carbon sequestration.