Definition: A Tier 1 ISP is an ISP that has access to the entire Internet Region solely via its free and reciprocal peering agreements.
Definition: An ISP is entity that provides (usually sells) access to the global Internet.
Definition: An Internet Region is a portion of the Internet network typically bounded by a country's geographical boundaries.
Each Internet Region has its own set of "Tier 1 ISPs."
A Tier 1 ISP by definition doesn't pay transit fees to anyone to reach any destination in the Internet Region.While we can see adjacencie in the Internet routing tables, it is difficult to determine if money is changing hands.Having said that, it is clear that most people in the Internet engineering communities know who the Tier 1 ISPs are for their Internet Region.
The litmus test is, "Does this ISP pay anyone (or barter) to reach any destination in the Internet Region?" If the answer is "No" then it is a "Tier 1 ISP" and if the answer is "Yes" then it is a "Tier 2 ISP."
Here is a partial list of Tier 1 ISPs across the world based on my conversations with Internet engineers. (I am sure that I am missing some.)
In the U.S. the Tier 1 ISPs (aka "The Tier 1 Club") include:
In Singapore the Tier 1 ISPs (aka "The Holy Trinity") are:
In Japan the Tier 1 ISPs are:
In Hong Kong the Tier 1 ISPs are:
In Australia the Tier 1 ISPs (aka "The Gang of Four") are
In New Zealand the Tier 1 ISPs are
In China the Tier 1 ISPs are
In Holland the Tier 1 ISP is
In Sweden the Tier 1 ISP is
In Finland the Tier 1 ISP is
In Turkey the Tier 1 ISPs are
In India the Tier 1 ISPs are
In Germany the Tier 1 ISP is
In South Africa the Tier 1 ISPs are
In Ghana the Tier 1 ISP is
In Spain the Tier 1 ISP is
In France the Tier 1 ISP is
* - Not verified
** - Not sure what happened to Reach and its Tier 1 peering in HK