For how many years will existing oil reserves cover demand?

Non-renewability of the fossil fuels that have powered world economic development over the last 150 years leads to pressing technical, environmental, and policy issues with respect to their continued use. Especially for oil, concerns arise regarding growth in demand in the developing world and the resulting duration of supply (and levels of price) in a global market.
Natural gas has growing prospects for use based on the greater potential of gas resource development, but its current limited adaptability to transportation uses and distribution infrastructure requirements are impediments to oil-natural gas substitution. Coal combustion for electric generation raises concerns over multiple types of emissions and global climate change, but coal gasification with carbon dioxide sequestration is an alternative. How quickly we creatively address fossil fuel depletion is a function of economics, policy, and technologies for use of the specific fuel.
Predicting that depletion brings up the question of accuracy of resource assessments, especially for oil, whose proved reserve base is the smallest in terms of years of future consumption. In 2003, oil represented 42.5 percent of world fossil fuel usage.
Global dependency, the concentration of conventional oil supplies in politically unstable regions, and limited ability to substitute other fuels in near-term transportation applications thus represent potential societal vulnerabilities. Predictions of peak oil deliverability in this decade and post-9/11 political realities increase concerns.
However, other views, based on refined resource assessment methodologies and the development potential of mature petroleum provinces, suggest that we may yet be several decades away from resource constraints on deliverability of conventional oil. Conservation, efficiency gains, unconventional oil resource development, natural gas-to-liquids, and coal conversion may further add to our time frame for developing significant alternatives to fossil fuels.
Fossil fuels - coal, oil and natural gas - are some of the world’s most coveted goods. As the need for energy continues to rise worldwide, rapidly industrializing and developed nations alike are grappling to ensure adequate supply levels. We wonder: Based on current trends, for how many years will existing oil reserves cover demand?
Coal has a longer lifespan than that of oil and natural gas combined. At current consumption rates, the world’s reserves of coal will last for about 150 years. However, the need for coal to power the developing economies of countries such as Brazil, India, Vietnam and China may diminish the fossil fuel’s projected lifespan.
In China, if the current rates of consumption and production continue, coal is likely to disappear in about 50 years. In 2007, the demand for coal in China alone increased 9% - and the country’s consumption now accounts for a quarter of the world’s total.
Provided the current rates of worldwide consumption and production continue, the supply of natural gas is projected to be depleted about 65 years from today (according to the BP Statistical Review of World Energy).
In 2006, the world’s natural gas consumption increased by 2.5%, while production grew an average of 3%. The greatest increase in production occurred in Africa - specifically in Egypt, Libya and Nigeria.
When considering the current rates of consumption and production around the world, oil’s lifespan currently stands at about 40 years. However, when including oil sands - deposits of oil found in layers of sand - the figure rises to about 50 years.
The prospect of new oil fields in Russia and the Middle East, while helpful, is unlikely to compensate sufficiently for the total decline in output at existing fields - and will likely fail to meet projected long-term consumption increases.