I've got to say I wondered about this myself and we try to make sure that DH gets it when he is out and about.

Thankfully we have a Mobil which is pay at pump, I think they are a great idea. I had to get petrol on Friday and the Mobil one was the dearest in our neck of the woods - $1.16 a litre! I was the only one there - needless to say, it's worth the little extra money not having to worry about bubs.