(3) - By Colin Campbells figures we have used 900 Billion Barrels (Gb) of oil, there are known reserves of 900 Gb and there are 200 Gb left to discover so the numbers speak for themselves. Today the world uses 30 Gb of oil every year, 24 billion barrels of conventional oil, with the remaining 6 billion coming from heavy oil and tar sands, deep water oil fields, and natural gas liquids (there are 42 US gallons in a barrel, or 159 litres). Oil stocks are declining at the rate of 2.2% per annum. At current levels of extraction we would run out of conventional oil in 35 years. The demand for oil is growing every year as emerging economies adopt our oil driven lifestyle. reports in wikapedia suggest that not all the oil can be extracted so some will have to stay in the ground.

Peak oil is also the point of maximum output, after a short plateau period the total output of conventional oil will go into steady decline, demand will not be met and prices will escalate.
Declining output reduces extraction rates and therefore extends the life of the well, Carbon and water can be pumped into the wells to try and maintain output rates, as oil prices rise this becomes more economic, however maintaining extraction rates will shorten the ultimate life of the field and this method may reduce the total recoverable figure.