You do not have to be a rocket scientist to understand the simple concept of depletion. Think of a glass of beer. The first sip tastes good, but your brow creases when the glass is half empty and you realise that you have drunk more than remains. When the glass is empty, all you can do is ask for another unless it is closing time. It is the same with oil.
Peak comes more or less at the midpoint of depletion, when the glass is half empty.
The reason why people don t understand the situation better is that the public data on reserves is grossly unreliable, subject to lax definition and poor reporting practices. The industry has systematically under-reported the size of discoveries for good regulatory and commercial reasons. Accordingly, the reported reserves have appeared to grow over time, giving the misleading impression that more was being found than was the case. In fact, the world consumes four barrels of conventional oil for every one it finds. The upward revision is mistakenly attributed to advances in technology when it is simply in the reporting.