Ok, so originally I hated these bottles because they leaked all over. But my baby has had really bad gas and I got desperate. How could there be so many good reviews if they all leak? What am I doing wrong? Turns out, the fill line "do not fill above this line" is obvious once you look for it. The directions "hold at 45 degrees and keep the vent end out of the milk" is much less obvious. Both are definitely complicated to figure out when you haven't slept properly in months. Bottom line is that they really reduce gas... but be careful how you hold them and fill them to feed you baby. If you're careful, they work like a charm.