I bought these for the purpose of carrying my own salad dressing in my purse, and they meet my needs perfectly.  They hold exactly two tablespoons, which is what I needed.  The seal is tight with no leakage at all.  I did not experience what some reviewers did with the lids not fitting well.  I took the advice of another reviewer and put these in a pot of boiling water for a couple of minutes.  I removed them with tongs and immediately put the seals on the container with no problem at all.  I left them on until they cooled.  Now the lids go on and off just the way you would want them too.  You don't want it to be too easy because then it will not be a tight enough seal.  Maybe it is a little tricky for young children as another reviewer pointed out, but for me it is relatively easy to seal them.  They are perfect for carrying a liquid ingredient without worrying about a leak.