Mine are the following...
"In 1900 (at the turn of the 20th century), what you see as oil became ubiquitous, population goes up in a vertical growth trajectory. We are at 6.5 billion people. We might be at 7 billion people by the time anyone sees this interview. All of these people exist on this planet only because of oil. That's it. So it is axiomatic that if you take the oil away, the population must also go away. In all of science, in all of biology, there is no case where any population (be it bacteria in a petri dish or caribou on an Arctic island) encounters favorable circumstances and goes on a vertical growth trajectory without an immediate crash down. It is a law. It is a law as fundamental as gravity. It is a law as fundamental as thermodynamics. And if one thinks of it, it might also be true of the stock exchange or financial markets which up like this (in a vertical line) and then go down like this. It is the history of every bubble"
by Michael Ruppert in the Collapse movie (2009)
"There is nothing in anywhere, in any combination, that can replace the edifice built by fossil fuels. Nothing".
by Michael Ruppert in the Collapse movie (2009)
"I do not believe we can sustain the current population of the globe, much less the population in 20 or 30 years, without the use of petrochemicals"
by David Goodstein in A Crude Awakening: The Oilcrash movie (2006)
"The problem we are facing is that there are too many people using up too much stuff, too quickly, and in an economy that only knows how to grow"
by Richard Heinberg
"What we should focus on is reducing per capita consumption of resources. Also, we should gradually decrease human population by the most humane means we can muster. This is very difficult to do because the right to reproduce is a sacred right in the eyes of most people. Especially to the religious right winged. But this has to be done. There is no other way."
by Richard Heinberg
I probably have several other favorite quotes from peak oil and sustainability advocates, but these are the few I can think of right now. I would like you guys to gather the best quotes from peak oil and sustainability activists.