Super-cycles of commodity prices since the mid-ninteenth century

Decomposition of real commodity prices suggests four super-cycles during 1865-2009 ranging between 30-40 years with amplitudes 20-40 percent higher or lower than the long-run trend. Non-oil price super-cycles follow world GDP, indicating they are essentially demand-determined; causality runs in the opposite direction for oil prices. The mean of each super-cycle of non-oil commodities is generally lower than for the previous cycle, supporting the Prebisch-Singer hypothesis. Tropical agriculture experienced the strongest and steepest long-term downward trend through the twentieth century, followed by non-tropical agriculture and metals, while real oil prices experienced a long-term upward trend, interrupted temporarily during the twentieth century.