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Irrigated rice (Oryza sativa L.) in West Africa covers about 12% of the regional rice-growing area, and is produced all along the agro-ecological gradient from the forest zone to the Sahara desert margins. Spatial and temporal variability of yield gaps (i.e., difference between actual and potential yield) were determined to set priorities for research and target technologies. On-farm trials were conducted on 191 irrigated lowland fields in the humid forest, the savanna and the Sahel. Farmers’ yields were compared with those of super-imposed treatments of improved fertilization and weed management. Farmers’ yields varied between 0.2 and 8.7 Mg ha(-1), with average yields of 3.4 Mg ha(-1) (Guinea savanna), 3.6 Mg ha(-1) (humid forest), 3.9 Mg ha(-1) (Sahel), and 5.1 Mg ha(-1) (Sudan savanna). Simulated potential yields increased from 7 Mg ha(-1) in the forest to about 10 Mg ha(-1) in the Sahel. Accordingly, yield gaps were large, ranging from 3.2 to 5.9 Mg ha(-1). Researcher weed control in the Sahel gave grain yield increases of about 1.0 Mg ha(-1). Improved weed and N fertilization management increased yields by 1 to 2 Mg ha(-1) in the forest and Guinea savanna sites. A share of 57-80% of the yield gap could not be accounted for. Improving weed control is likely to have the highest pay-off in the Sahel while improved management of fertilizer N will be most beneficial in the forest and savanna environments.