Comparative Transportation-Model Optimisation of Water Distribution under Post-Subsidy Freight Costs: A Delta State Case Study

Nigeria's May 2023 fuel-subsidy removal raised haulage costs sharply, strengthening the case for formal route-allocation over informal, experience-based distribution. This paper applies and compares four classical transportation-model procedures (North-West Corner (NWCM), Least-Cost (LCM), Vogel's Approximation (VAM), and the Modified Distribution (MODI) optimality test) to a simulated case study of a pure-water sachet factory operating three depots and four demand zones in Agbor, Delta State. Unlike comparable Nigerian case studies, the unit-cost matrix here is not judgementally assigned but derived from route distances, an assumed fuel-consumption rate, a representative diesel price, and a fixed handling charge, making the cost structure reproducible. On a balanced 3×4, 1,900-carton-per-week network, NWCM costs ₦100,650/week; LCM and VAM independently reach the same allocation, ₦86,750; MODI, applied through two stepping-stone iterations, finds a further-improving route and converges on the true optimum, ₦85,850, confirmed by a linear-programming solver. That LCM and VAM agree yet both fall short of optimal shows MODI is a necessary, not merely confirmatory, step. The MODI-verified allocation cuts weekly cost by 14.7% versus NWCM, consistent with the 10-40% range reported elsewhere. A 25%-diesel-price sensitivity check leaves the optimal routing unchanged, though not its cost. The paper situates this firm-level result against inconsistent published estimates of Nigeria's logistics-cost share of GDP, arguing firm-level optimisation is necessary but not sufficient for any macro-level target.