Facebook had another strong month across Asia and the Middle East, growing by 8.5% in January to reach 73.5 million monthly active users. But as with other parts of the world, many smaller countries that grew first are now maxing out; with large portions of their online populaces on Facebook, there’s no room left to grow.

Meanwhile, big countries in Asia are surging. Even though some have millions of users already, they have a lot of room left to grow. We’re seeing the same trend in Europe and other parts of the world.

Out of the 10 countries in Asia that gained the most users last month, 3 also made the top 10 worldwide: Indonesia, India and The Philippines. All of these countries have 10% or less of the country currently on Facebook. India, where Facebook social gaming leader Zynga is opening up its first international office, has the lowest, with less than a 1% rate.

Of course, there’s the question of what the total opportunity is here for Facebook to grow. In many countries, many people have basically no access to the internet. The catch is that mobile devices are increasingly making it possible for the service to reach more people. In Indonesia, Facebook executive Chamath Palihapitiya recently explained, nearly every user is on Facebook via their phones. Overall, the company says 100 million of its 400 million users access the service via mobile every month. And, to push usage even higher, it is planning to introduce a very simple mobile site, called Zero, that will give people access while using a bare-bones data connection.

For many more details, check out our Global Monitor report. Note that we get our data from Facebook’s advertiser tool. Although it typically shows the same trends as third-party analytics services, this data also tends to lag behind other projections.