One aspect of the current economic difficulty that argues that the future may not be like the past is the cost of energy. The chart below shows U.S. fuel cost as a percent of GDP. Historically, fuel cost has been in the range of 3 or 4% of GDP. This percent spiked to nearly 10% in the late 70s, and times were somewhat hard then. For several reasons, including oil discoveries in the North Sea and Mexico, nuclear power coming on line, and some energy-intensive industry leaving the U.S., this percent dropped back down. Now it is rising again. If global petroleum production has peaked and begun to decline as some argue (see, especially, writings of Ken Deffeyes, Colin Campbell, David Goodstein, and Jim Kunstler) the price of oil will rise, and the percent of GDP spent on fuel will grow. Obviously, we cannot spend 100% of GDP on fuel. Can the economy function normally if we're spending 6%, 10%, 15%? Stay tuned.