While many blame speculation for rising oil prices, the document summarizes that supply constraints are increasingly evident as the largest low-cost oil fields have matured and new discoveries are smaller and more expensive. The relatively small size of the crude oil futures market means it is susceptible to large price swings from rising investor interest, though it is difficult to distinguish speculative investments from those reflecting recognition of tight supply and demand fundamentals. US consumer spending on energy reached 20-year highs in 2008, though some signs of declining demand growth emerged, and most global demand growth came from developing countries like China and Saudi Arabia.