This is part of Heading Out's Sunday tech talk series.

I am going to insert a topic here before going on to Carbonates, as I had mentioned doing in the last post, because it will help to explain a developing problem that comes when extracting oil from rocks such as chalk. And, because I used this example in my original post, let me again start by creating an analogy.

The oil business is one of great complexity and there are some challenges even in trying to explain some of the basic reasons why, when price goes up, producers can't just turn a tap and pull more oil out of the underground reservoir.

I was trying to think of a way of explaining it, and offer the following, in the hope that not too many of those who know reality will be offended at the simplification.

Way back at the beginning of the current Elizabethan era it used to be fun, after dinner, to float cream on top of coffee. I still do it when the cream is of the right sort, and it gives the coffee a different taste. Putting the cream over the coffee is a bit of a challenge, you start by using the back of a spoon, and when you get better pour it down the side of the cup.

As you may have noticed President Bush commented this past week on his (and apparently their) doubts that Saudi Arabia could significantly increase crude oil production. While this comes as no great surprise to those of you that have been reading Stuart and Euan’s excellent articles, I thought I would try and summarize the situation as I see it, and expand a little beyond the short summary paragraphs that Leanan is providing, to give more of an overall picture.

To begin you should know that when the Kingdom of Saudi Arabia (KSA) talks about the size of their oilfields, they refer to the amount of oil that was there at the beginning, rather than that which is left. You can do this calculation for yourself, but I exemplified it with a small calculation on the amount of oil that originally existed in the Abqaiq field , by making some simple assumptions.

I learned, to begin with that

Although it seems straightforward, depletion as a concept is not easy to pin down. The very use of the word "depletion" in this context - synonymous as it is with exhaustion - implies that oil resources are being run down and that one day they will dwindle into insignificance. Oil resources may well become insignificant in the years to come, but it is not certain whether this will be due to their physical exhaustion or to the world moving away from oil and towards another source of energy.