Abstract Combining deterministic and probabilistic procedures, the economics and commerciality of steam-assisted gravity drainage (SAGD) for exploiting the Nigerian heavy-oil sands are investigated. Considering net present value (NPV) and value–investment ratio as the objective functions, the impacts of reservoir performance, costs, oil price and fiscal regime are evaluated. Within the range examined, reservoir performance, oil price, and expenditure profiles are found to be the primary determinants of project value and risks. For the case studied, SAGD has more than 75% chance of economic success (NPV>0), suggesting its attractiveness for the Nigerian bitumen deposit. However, potential risks are highlighted, and mitigation measures prescribed.