The Rollover

Recent data from Colin Campbell at ASPO, one of the world's most experienced in the study of peak oil, indicate that the peak extraction of oil will occur around 2012 (See diagram below).After this date (give or take two or three years, depending on the extraction capacity of the Russian oil fields), a sharp increase in absolute fuel prices can be expected, since demand will exceed supply.To fill the gap between demand (dotted line, assuming a 1% increase p.a.) and supply might be extemey hard. Below is a calculation how many nuclear plant that would be needed.
If you prefer wind power plants, just add three zeros to the figures of nuclear reactors.

The upper curve is the sum of all liquid petrochemical products (conventional oil plus condensate, liquified coal and the like).
The lower curve is conventional oil. (p.a. = per anuum)When the extraction of oil not longer can meet the demand around 2012, a sharp increase in price might be expected.

An estimate of the carrying capacity for humans on Earth without fossil fuels.

The theoretical demand of liquid fuels is assumed to increase 1% annually after 2004 (historical average, however, IEA assumes 1.7%).
If we assume, for a moment, that our energy requirements for transportation (aeroplanes, ships, cars) could be provided by electricity, about 6,300 new nuclear reactors would be needed by 2031, and with an (increasing) annual production of 520 additional new nuclear reactors per year, globally.The cost of building these new reactors would be about 40% of the US GNP of 2002.
Given that you can fuel them. The Uranium is in itself a limited resource, and it is mainly extracted by means of fossil fuels.
If you are interested in wind turbines, just add 000 to the number of nuclear reactors.
So the problem is not only to find new energy sources, but also to implement them successfully.
May be a solution could be a rapid adaptation to a lower access of energy?

Actually, quite recently, a full-scale experiment on oil depletion on an industrialized society was made, using North Korea and Cuba

The result was that a highly specialized, export-import based agriculture succumbed, but one based on organnic growing for local production suvrived.