If you are an online PSP, eCommerce volume  is one of the main criterion to look at where to expand internationally.  Of course, growth rates, competition, payment types, fraud management, etc. are important determining factors, but here is just a view of the relative sizes of online payments (b2c only):

 PS: Don't pay very close attention to the exact numbers. Different surveys and reports come up with different numbers. This will, however, a rough idea on the relative sizes..

The most important country specific knowledge you need to have before expanding your services in a new country at a 50,000 feet is:

Here is a quick snapshot of the payment scenarios in some big non-US markets. Note that because of the online-offline convergence, we need to look at what's happening online as well as retail markets.

And finally,  here is a look at the credit card/debit card trends in those regions. One can see the usage trends and based on that decide what payment instruments to support when expanding to those countries.

Here is a glance at the worldwide PSPs.. Most of the US and European PSPs provide services in other markets as well. Have listed some regional players as well in those countries..

This post can never be comprehensive and will always be work-in-progress, but I hope you can get an idea of the state of the PSPs in some important parts of the world.

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