It appears that light sweet crude has already peaked, and production is bigger than ever which means that more and more production is sour crude. This crude is harder to refine, which is a problem since many refineries are not equipped to refine it, and needs to upgrade in order to do so. The low number of available refineries equipped and the cost of rebuilding them, seems to be a big reason for the rise in fuel prices.
I am not sure if it can be accurately estimated how much oil we have, as technology develop which help exploit more oil from existent oil fields as well as discovering new sources; the Brazilian deep-sea oil found recently as well as the massive potential Greenland oil reserves. The Athabasca oil sands in Alberta is a also a massive source of oil; extraction of this heavy sour comes with devastating environmental impact.
With demand only rising in the whole world – notably from China and India – it seems hard to judge when total peak oil will happen.
There is a Russian alternative theory of the creation of oil that contradicts the theory of fossil oil being the one and only. They mean that there are huge amounts of abiogenic petroleum deposits deep in the earth, created at the time of formation of the planet, and that this oil seeps up and replenishes surface oil sources. Few support this theory, but it resurfaces regularly. It’s possible, but doesn’t seem likely.
I am not sure if anyone knows if we will have oil for 30 years or 100 years. We will probably only know of total peak oil when it plateaus and declines. Everything else seems to be educated guesses.
Hopefully someone else will give you a clearer answer.