Originally Posted by NM
But its much harder to come to a conclusion about the economy cabin since there are so many more seats covered by those fare buckets. The best indicator is the availability of the heavily discounted fares such as N, O, Q and the award seats X and T. None of these are available for the outbound flight, so there may be as few as 9 seats left in economy.
I agree with this, but would add the caveat that I've seen flights looking like this on availability displays when I know that they're already overbooked.