Coal the most abundant fossil fuel

Deposits of coal are dispersed across all large land-masses. Estimates of total accessible reserves indicate that the amounts are sufficient to meet projected needs during the next three to five centuries. The uncertainty in this estimate arises in forecasting the ease of extraction because many seams are thin, necessitating the removal of large amounts of rock. The economic value of coal also depends on location, calorific value and concentrations of undesirable impurities (including sulfur). 

In 1991, the total coal reserves were estimated to be about five times greater than the equivalent petroleum reserves and six times greater than the reserves of natural gas (based on calorific value). Petroleum and natural gas reserves combined have been projected to be capable of supplying energy demands for about 50 years. 

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