Despite extensive literature on contributing factors to the high commodityprices and volatility in the recent years, few have examined these causalfactors together in one analysis. We quantify empirically the relativeimportance of three factors: global demand, speculation, and energyprices/policy in explaining corn price volatility. A structural vectorauto-regression model is developed and variance decomposition is applied tomeasure the contribution of each factor in explaining corn price variation.We find that speculation is important, but only in the short run. However,in the long run, energy is the most important followed by global demand.