We introduce simple production economic models to estimate the potential gains from mergers. We decompose the gains into technical efficiency, size (scale) and harmony (mix) gains, and we discuss alternative ways to capture these gains. We propose to approximate the production processes using the non-parametric Data Envelopment Analysis (DEA) approach, and we use the resulting operational approach to estimate the potential gains from merging agricultural extension offices in Denmark. Table of Contents: 1. Introduction, 2. Literature, 3. Production Models, 4. Measures of Merger Gains, 5. Decomposing Merger Gains, 6. Alternative Decompositions, 7. The Danish Agricultural Extension Services, 8. Final Remarks, References. Key Words: Data Envelopment Analysis, management, organization, mergers