Bruce Sterling Woodcock of MMOGChart has been tracking the subscriber numbers for a variety of different MMOs for years; version 19.0 of his data was released about a week ago, providing numbers up to January 2006 in a long-awaited update. The chart's coverage isn't perfect; geographic information would be especially useful, but is near impossible to find, and the site explains the accuracy behind the data (there are differences between active subscribers, cumulative subscribers and boxes sold). However, it's interesting to see what this snapshot of the current MMO world is like.
The graph above shows the largest MMOs, those with over 120,000 subscribers. The green line leaping towards infinity is World of Warcraft -- the yellow and red curves, declining slowly, are Lineage and Lineage II respectively. Many of the others stop in 2005, so it's hard to get an accurate up-to-date picture, but the light blue line representing Runescape seems to be finally taking off, cresting the 500,000 barrier -- an impressive feat for a game started by a couple of students.
In contrast, the smallest MMOs, shown above, paint a picture of growth, loss, and death. EVE Online (orange) is shooting up, as is Second Life (peach); The Sims Online (yellow) and Asheron's Call (purple) are both past their prime. Others, like A Tale in the Desert (navy) are keeping a constant pace for years -- neither attracting new subscribers or losing current ones. Given the low numbers involved, this might not be self-sustaining for much longer, although it is healthier than the rapid downward trends we see in other MMOs.
As this pie-chart of market share division shows, World of Warcraft is clearly king of the MMO scene at the moment, with Lineage and Lineage II grimly hanging on to large subscriber bases. However, the charts show a turbulent history for various MMOs, and things may change drastically in the future. The current market is overwhelmed with the fantasy genre; perhaps new genre experiments such as Auto Assault will rid the world of its huge preoccupation with elves and orcs, or perhaps some of the smaller MMOs racking up subscriber growth at the moment will get very large indeed.