I don't know who pushed the idea that petrol could get to...

I don't know who pushed the idea that petrol could get to $8/litre but what a moron he is. All the morons are falling for the obscurantism that oil will keep going higher and higher. This is simply pure evil as nobody is that retarded to believe that.
The reason oil has a finite limit (about $200/barrel) is that there is more oil in tar sands and oil shale than there has been oil in the Middle East. It will last us many many centuries. It hasn't been developed because it has been uneconomic. HOWEVER, we are fast approaching the point where it becomes profitable. The problem is that OPEC could simply drop the price of oil if a competitive source becomes available. Hence the western world has to develop these sources of oil and ban the purchase of Middle East oil. When that happens we have a stable source of fuel and a stable world economy. I don't think this will happen so OPEC will push the price of oil to this point but not much beyond.