If you didn't catch it, read my intro post below. There's also some links in there to primers, etc.
This post, however, will be an attempt to sum up a pretty complex topic.
Hubbert's Peak is reached when demand for oil
exceeds production and supply.
Let's be clear, peak oil is not about running out of oil. However, there is a finite amount of oil in the earth. At some point, we will have taken half of it. That is Hubbert's Peak.