A field experiment was conducted during the winter season of 2002-2003 and 2003-2004 at Baruipur, West Bengal, to evaluate herbage productivity and economic feasibility of oat (Avena sariva)-based intercropping system with mustard and legumes under varying fertility levels in Gangetic alluvial (Entisol) soil. Paired row planting (20/40 cm) of oat intercropped with lobia (Vigna sinensis L.) (1 row) recorded the highest green forage (59.73 tonnes/ha), dry fodder (19.05 tonnes/ha), crude protein yield (4.5 tonnes/ha) and net returns (Rs 18 785/ha) compared with other sole and intercropping systems. This treatment produced 24, 74 and 12% more green forage, dry matter and protein content of oat respectively over sole oat in normal planting. Application of 120 kg N, 25.8 kg P and 33.2 kg K/ha gave highest green forage and dry matter yield, crude protein content, crude protein yield, N-uptake, net return and monetary advantage compared with other fertility levels.