Bullwhip Buster — Siam Pantry's Four-Tier Supply Chain

A four-round, advanced operations and supply-chain simulation set inside Siam Pantry Co., Ltd., a THB 4.2 billion Thai manufacturer-distributor of instant noodles, ready-to-drink coffee and sauces that sells through a classic four-tier chain — factory → regional distribution centres → wholesalers → modern-trade and traditional retailers. End-consumer demand varies only ±6% week to week, yet factory production orders swing ±48% in normal weeks and spiked +62% after a single four-week price promotion: a textbook bullwhip effect. The company carries THB 620M of inventory at a 9% cost of capital, still suffered stockouts in 11% of outlets during the promotion, runs a 38% factory forecast error (MAPE) against a 15% best-practice target, and absorbed THB 240M of excess stock plus THB 31M of write-offs. Playing the Operations Strategist, the learner must dampen the amplification without breaching an THB 18M/year coordination-and-systems budget or dropping service. Round 1: diagnose the bullwhip — compute the variance amplification ratio tier by tier and rank its four classic causes (demand-signal processing, order batching, price-promotion swings, rationing and shortage gaming). Round 2: the core design — choose an ordering policy (independent reorder-point, smaller more-frequent orders, base-stock with order smoothing, or coordinated replenishment), an information-sharing level (none, POS-data sharing, shared forecast, or VMI/CPFR), and a promotion policy (deep periodic discounts, scheduled capacity-aware promos, or everyday-low-price), each consuming budget and changing variance, cost and service. Round 3: stress-test the design against live shocks — a viral demand spike, a lead-time disruption, and a key wholesaler refusing to share POS data — and patch it with a fallback and a shock-response rule. Round 4: present the board-and-partner scorecard, forecasting order variance, inventory cost, service level and forecast error within the THB 18M budget. The math rewards coordination and information-sharing over inventory accumulation, complementary policy-plus-information design, smoothing that stays responsive to a real surge, contingencies for non-cooperating partners, and disciplined promotion policy — and punishes the six classic errors: piling safety stock at every tier, smoothing orders without sharing demand, over-smoothing into a stockout, assuming free POS visibility, keeping deep promos that re-trigger the whipsaw, and over-spending the coordination budget. Final KPIs track factory order variance (%), inventory cost (THB M/year), service level (%) and forecast error (MAPE %).