Colin Campbell is a British petroleum geologist who founded the Association for the Study of Peak Oil (ASPO) and many people use their research and newsletters for understanding the Peak Oil problem (including myself). In 2002, Campbell put out what he called The Oil Depletion Protocol, a relatively short document, but hard to understand. Richard Heinberg, currently the established "guru" on the problem, set out to explain the protocol, amplify it and bring it to a wider audience by writing The Oil Depletion Protocol in 2006. It is a relatively short book, but well-written and full of useful numbers.
For example, page 23 of The Oil Depletion Protocol lists several authors and their dates of the onset of peak oil. These numbers range from the years 2005 to 2030. Page 117 has a startling statistic, "Nitrogen fertilizer, made from natural gas, accounts for 47 percent of total energy usage for corn farming in the American Midwest." There is also an accompanying table listing a nine-state weighted average for total energy requirements to produce corn in 2001, including seed, fertilizer, fuel for hauling, and irrigation. This figure is 49,573 BTU/bushel. Since a bushel of corn weighs 56 pounds, this is 885.23 BTU/pound. Since a BTU = .252 kilocalories, there were 223 kilocalories needed to produce one pound of corn in the American Midwest in 2001. This figure is likely higher now, as one of the features of chemical fertilizers is that more chemicals are needed each year to maintain the same level of production. [Sidebar: Using organic fertilizers requires less fertilizer each year as the soil is built up to sustainable levels. Part of this process is crop rotations and green manures.]
It should be noted that this number of kilocalories (or "calories" as we usually refer to them - some researchers use the term "large" calories - it is the number on the side of your cereal box) is just for getting the corn to the elevator. Once the corn is processed and made into high-fructose corn syrup, cornflakes, or cattle feed, the calorie load becomes much higher because more energy is needed to make the field corn into a value-added product. [Sidebar: If you think of meat as a value-added product, a lot of the marketing and cultural mythos becomes easier to understand - especially the class stratification aspects.]
Anyway, back to Heinberg's book. The Oil Depletion Protocol is quite an easy read, as Heinberg's writing style is quite lucid. He also hits the main points quite well. The book is certainly disturbing, however, as any sober assessment of the facts about peak oil becomes more disturbing the more research you do. The main advantage of the book is unintentional. Implementing the Protocol would require a huge sea change in human consciousness and a retreat from the growth model. This is unlikely and possibly impossible, as it would require the US and all other developed countries to go back to a pre-1850's lifestyle. So, going along with our present dependence on fossil fuels is impossible because of the laws of physics. Changing enough to actually get off our addiction to oil is impossible because we have too many people on the planet to support without our oil addiction. This is also unlikely given the past history of human cultures around the globe. Even the developing countries like India and China, who should know better, want to develop their industries and infrastructure as much as they can. In short, the Protocol is a nice idea, but not doable. It shows us instead how unrealistic the present governmental structure really is, in all the countries around the globe. In other words, the indirect lesson of The Oil Depletion Protocol is that we have to do it ourselves, on a local level.