Petrol price cycle

When I eat breakfast I usually watch TV. In the morning I like to see the news. To me it's a good start of the day to get some orientation about what's happening in Australia and the world overseas.
However, I have come across one strange thing...
In the financial part of the morning news, besides reporting share prices, market indexes and currencies, they also report the current petrol price. Well, a little bit odd maybe you could think but not really that strange. The strange thing is that the price is always accompanied by a comment about where we are in the price cycle. Hmmm which price cycle? How can a serious journalist in advance say he/she knows where in a cycle we currently are?

As a recently become car owner of course petrol price is of interest so I started to research. And surprisingly enough it turns out that petrol prices vary up in down in obvious cycles in Oz. And it's not small variations. We are talking about 20%! How this can happen in a free market I don't understand but I guess it's just to accept and adapt your filling pattern!
The graph shows price in Sydney over the last 45 days.

And below it is. Our ticket to freedom. The Silver Pearl!!

Cheers!