The end of the petroleum age will not be "when all the oils runs out." Rather, the dividing line between the energy past which we know and the post-petroleum era the outlines of which remain dim will be much more subtle. It will be the point where the amount of oil consumed in exploring and producing new oil wells exceeds the amount of oil which the wells produce.
"We could be very close to this break-even point . . . when you take everything into account," says Charles A. S. Hall, a Cornell University ecologist.
Dr. Hall, with his colleague Cutler Cleveland, wrote a "net energy" analysis of US petroleum production which appeared in Science, the journal of the American Association for the Advancement of Science, last month. Net energy is the amount of energy produced relative to the amount of fuel needed to produce it.
The two biologists found that the number of feet of well required to find a barrel of oil and the amount of energy consumed in the oil field for every barrel discovered have been increasing since 1945.
Projecting these trends into the future, they found that somewhere between the years 2000 and 2007 more energy will be used in finding and producing new oil and natural gas reserves than will be produced in the fuels pumped out of the ground. The study also shows that the more intensely industry searches for oil and gas, the sooner this break-even point will be reached.
"Our analysis is a conservative one because we did not include the energy used by workers commuting to and from the site, the energy consumed in refining, or that used in distributing these fuels from the field to the point where it is used," Mr. Hall says.
However, viewing society's activity from a net energy basis is still a new and somewhat controversial perspective. Oil company representatives and economists, in particular, tend to play down its importance.
"It's really a matter of dollars. People exchange dollars for gasoline. We explore for oil and gas because we thinik we can make a profit," says William McCampbell, an ARCO physicist.
Industry representatives generally argue that the cost of finding new oil and gas includes the cost of the energy consumed in the process. Thus, at the point where it takes more energy to develop new wells than they produce, oil exploration automatically becomes uneconomical. "We do spend some time worrying about when that point will come," Dr. McCampbell admits.
Net energy advocates, on the other hand, find this economic rationale unconvincing. Hall points out that the actual cost of oil exploration can be distorted by several factors:
* Some companies are using 10-year-old drilling rigs which were built with substantially less expensive energy than they would require today.
* Some companies also burn old oil -- which is kept at an artifically low price -- to generate electricity to drill for new oil which sells at a decontrolled price.
* Industry profits are also influenced by tax laws and loopholes.
Because of this, net energy analyses can be useful. But these studies are themselves far from prefect. They involve a number of assumptions and approximations, and these are usually open to criticism.
In the analysis by Hall and Cleveland, for example, the scientists took industrywide data on annual drilling rates and divided this into the year's petroleum discoveries. They got a ratio which varied widely and approximated it with a straight line. They did the same thing with energy cost of drilling and extracting oil and gas. Then they projected these lines 30 years into the future.
"What really bothers me about this analysis is the linear projection," says McCampbell. "It may be a good statistical fit, but you have to be very cautious of statistical relationships like this, if there is no apparent physical cause underlying them."
But the two biologists do feel there are underlying causes, such as the necessity to drill deeper to find oil and gas and the increasing prevalence of smaller reservoirs.
McCampbell counters that in the last two years the average depth of wells drilled has been less than that of the preceding years.
Furthermore, there are a number of easily tapped reservoirs, such as tight sands natural gas deposits, which have become economically attractive and produce for 20 years or more, argues McCampbell.
Still, it is a matter of "When" rather than "if" oil will cease to be the primary fuel for the world. And "we won't know that fo r sure until we're old men." says Hall, wryly.