Cereal, oilseed, and protein (COP) production is an important sector contributing to Sustainable Development Goals (SDGs) in Tunisia. COP farms often diversify their production patterns to stabilize their income sources and spread production risk across crops. However, crop diversity may entail an inefficient use and management of resources to achieve the desired output. In addition, the COP sector still shows a low productivity level, depending on weather conditions in Tunisia. In this context, this study aimed to assess the relationship between the land use pattern and efficiency performance of farms. We used data envelopment analysis (DEA) in the presence of uncertainty based on state-contingent techniques. This approach has not previously been used to examine the links between crop pattern and efficiency. We found that specialized COP farms, on average, exhibited higher technical efficiency levels than those adopted mix cropping systems (83% and 60%, respectively), indicating an important margin to reduce inefficiency. Nevertheless, both diversified and specialized farms could reduce their inefficiency levels through more rational input use to attain the current level of production. Some practical implications were derived to target policy interventions to enhance agricultural productivity and resource use efficiency.