To improve national food security, successive Mali governments have always focused on expanding and intensifying production in the government-managed irrigation schemes (Office du Niger), which account for about 50% of domestic rice production. Because the cost of expanding and rehabilitating those schemes is high, the government is looking for complementary cost-effective ways to achieve this goal. The government could increase domestic rice supply by investing in improving the farmer-managed inland valley swamps. Although the government has paid little attention to those marginal lands, farmers have been growing rice in these areas using traditional technologies. This paper used data from a survey of 334 bas-fond farmers and secondary data to examine the potential contribution that these undeveloped bas-fonds could make to improve food security and rice exports in Mali. The study found that, if fully developed, the bas-fonds and flooded plains could produce more rice than is currently being supplied by the Office du Niger, or imported through commercial imports or food aid. As expected, rice yields in the bas-fonds are lower than in the Office du Niger. However, bas-fonds rice production is both financially profitable and provides a higher return per day of family labor than the competing upland crops (maize, sorghum/millet and cotton). In addition, the estimated domestic resources cost ratios show that, compared to the Office d u Niger, bas-fond rice production represents a better use of domestic resources, both for producing rice for home consumption and for the market.