lady bug
The bottle liners are awesome.. they do sell special bottles for them (they don't have a bottom). It does help with the gas, because you can push the air out before you put the top on... plus they can hold the bottle their self a lot earlier, because they don't have to hold it up.

keonlisen
I use the playtex bottles with liners, and you can use both the molded and the unmolded types. I find the ones that aren't molded better because, while they say that they're already sanitized, I wonder how it can still be clean after you open the box and the molded ones have those huge gaping entrances that can easily collect dust. THe others need to be opened up and pulled apart right before you add the formula. That's just me though. I started with the molded ones adn converted due to financial reasons, but I prefer the unmolded ones. The nursers are meant to be able to use both the molded and unmolded ones. I also used the Avent liners (they were given to me) in the playtex nursers and there seems to be no problem. It does help prevent my son from swallowing air and he won't use any other bottle. He gets gassy once in a while, but now at 4 months, I think he's only been gassy about 5 times. Also, you can pretty much put the liners into any bottles, as long as it fits the mouth of the bottle. I did this with another bottle set and it worked just fine.

E M
Yes you should buy the bottles that are used with the liners. We use the playtex drop in system. It doesn't matter if you use the pre-formed ones or the bag type. They do help with gas because you can squeeze all the air out of the liner before giving the bottle to the child. We use these bottles with our 9 month old twins and have since birth. I highly recommend them.

oh_froggit
i would definitely use the bottles that are made to be used with liners. another thing you might like to try is the playtex vent aire bottles...they don't use liners, but they have a special rubber piece in the bottom that allows air to flow, so they baby doesn't end up swallowing air bubbles. they REALLY do reduce gas and spit up, they were fantastic for my son, and i LOVE them.