Simply put, oil is a fossil fuel. We are extracting oil out of the ground at an incredibly fast rate. The 'peak' is when half of the oil is used. Out of the top 65 oil producing countries, 54 are past their peak and are now in decline.
As this graph shows we simply aren't finding enough oil to fill our insatiable demand.
Lots of articles, websites and lectures have been put together to make sense of it all.
Try this article on Richard Heinberg in the SMH; http://www.smh.com.au/news/national/when-oil-dries-up/2006/08/25/1156012745906.html?page=fullpage#contentSwap3
Richard's talks can be downloaded onto mp3. Well worth listening to. Try this one; http://www.globalpublicmedia.com/lectures/446
Watch the ABC TV Four Corners broadband edition on Peak Oil; http://abc.net.au/4corners/special_eds/20060710/
Or ABC's Catalyst program; http://www.abc.net.au/catalyst/stories/s1515141.htm
Visit ASPO (Australian Association for the study of Peak Oil and Gas); http://www.aspo-australia.org.au/
Sydney Peak Oil has a site; http://www.sydneypeakoil.com
And, go here too... http://www.eclipsenow.org/