It’s common knowledge in the U.S. search industry that Google has a market share of about 65 percent.  Lots of people know (or at least know how to check) the search giant’s market cap, too (it’s currently at $180 billion).  But another measure of Google’s size was presented yesterday, and it turns out that Google is on par with all but the biggest ISPs.

Craig Labovitz, Chief Scientist of Arbor Networks, stated on his company’s blog, "If Google were an ISP, it would be the fastest growing and third largest global carrier.  Only two other providers (both of whom carry significant volumes of Google transit) contribute more inter-domain traffic.  But unlike most global carriers (i.e. the ‘tier1s’), Google’s backbone does not deliver traffic on behalf of millions of subscribers nor thousands of regional networks and large enterprises.  Google’s infrastructure supports, well, only Google."

Those are some fairly astonishing observations.  Then here’s another fascinating tidbit: Labovitz continued, "Based on anonymous data from 110 ISPs around the world, we estimate Google contributes somewhere between 6-10% of all Internet traffic globally as of the of summer of 2009."

It’s hard not to see Google’s fiber network experiments in a different light after absorbing this information.  The company might not just thrill the residents of a few towns and make ISPs nervous; Google really does appear capable of changing how the industry works, and may even be able to do so without breaking a figurative sweat.

We’ll be sure to keep an eye on ISPs’ reactions as Google moves ahead with its tests.