The status of world oil reserves is a contentious issue, polarised between advocates of peak oil who believe production will soon decline, and major oil companies that say there is enough oil to last for decades. In reality, much of the disagreement can be resolved through clear definition of the grade, type, and reporting framework used to estimate oil reserve volumes. While there is certainly vast amounts of fossil fuel resources left in the ground, the volume of oil that can be commercially exploited at prices the global economy has become accustomed to is limited and will soon decline. The result is that oil may soon shift from a demand-led market to a supply constrained market. The capacity to meet the services provided by future liquid fuel demand is contingent upon the rapid and immediate diversification of the liquid fuel mix, the transition to alternative energy carriers where appropriate, and demand side measures such as behavioural change and adaptation. The successful transition to a poly-fuel economy will also be judged on the adequate mitigation of environmental and social costs. (C) 2010 Elsevier Ltd. All rights reserved.