Irrigated rice farming in the Senegal River Valley is known to be highly productive, as indicated by the average yield of nearly 5 tons per hectare, and the extensive adoption of modern seed-fertilizer technology. This study seeks to understand why rice farming is so productive in this region; analyzing this situation from the viewpoint of the management efficiency of large versus small scale irrigation schemes. Contrary to popular belief, the study found that farmers in large-scale irrigation schemes achieve significantly higher yields and profits than those in small-scale irrigation schemes.