Early this year I got a 3 pack of Avent bottles. All 3 of them leaked, About a month ago, at the other side of the country I bought another pack, thinking maybe it was just a faulty pack, these ones also leaked, more than the first pack did.
I looked online and someone said you have to get the fins set in the right place for the correct air flow without leaking. I checked that but it doesn't apply to these, as they are newer and have a special ring that is supposed to prevent leaking.
Also I tried screwing the top very tight, or a little loose, but still leaking either way.