R.C.
Hi,
It is totally normal for one breast to produce more than the other. Another possibility might be that one breast simply has a faster flow, so it takes longer for the slower breast to empty. This is the situation with me. I've been pumping for 18+ months, and I used to think my left breast produced less than my right. I realized, however, that my right simply empties faster, and if I give the left one enough time, it produces the same amount as the right one. In any case, as long as you continue to empty the breast that is producing less, it will still continue producing milk, so you don't have to worry about that.
Hope that helps!