In this paper, we analyze data on the opinion dynamics of 1,660,927 users of an online social network using formal models of opinion formation. We have observed that moderate users have a tendency to follow the average opinion of their online friends, which we interpret as a presence of bounded confidence. Further, we have discovered that the probability of moving toward the average opinion goes down if the difference between it and the user’s opinion is too large. Another interesting feature uncovered is that if a user’s opinion and the average opinion of their online friends are very similar, the influence also decreases.