Teaser 2566: A fulfilling strategy

From The Sunday Times, 27th November 2011 [link]

I drove down a road with a number of petrol stations whose locations I saw on my map. I decided to check the price at the first station then fill up when I found one offering a lower price (or, failing that, the last one).

When I got home I noticed that I could arrange the prices (in pence per per litre) into an ascending sequence of consecutive whole numbers of pence, plus 0.9p (i.e. 130.9p, 131.9p, 132.2p, etc). I also worked out the average price that I would expect to pay using this strategy, if I were to encounter this set of prices in an unknown order, and I was surprised to find that this value turned out to be a whole number of pence per litre.

How many petrol stations were there?

When the puzzle was originally published in The Sunday Times it had been edited into a form that meant there were no solutions. Here I have rephrased the middle paragraph so that it works as the setter originally intended.