In a context where agricultural production systems are being questioned because of their environmental impacts, crop-livestock farming is often presented as an agro- ecological model that could conciliate agricultural production and the environment. However, there is no consensus on the appropriate strategies to be favored to achieve this objective. This paper contributes to the underlying debates by analyzing the opportunity cost of providing environmental services in mixed crop-livestock farming to investigate whether the double objective of agricultural production and provision of environmental services is feasible without monetary incentives and to infer the conditions under which it is achievable. We develop an original analytical framework to estimate farm-level production possibility frontiers, which includes both agricultural production and environmental services, while relaxing the traditional non-negativity assumption of the opportunity costs of environmental services. Using a French dataset, we find that the opportunity costs of the indicators of environmental services considered are mostly negative. This suggests that the environmentally friendly practices associated with these services generate gains for farmers. Results from econometric estimations show that the share of the agricultural area in grasslands, the share of autonomous beef production, a high labor intensity, and direct payments increase the probability of having non-positive opportunity costs.