Have the exchanges disclosed their criteria?
Does anyone have a best guess based upon observations of volume (however you wish to define it)?
Please no qualitative answers.
You are referring to the Penny Pilot Program. Only options whose premiums are quoted at a price less than \$3 may be eligible for penny increments, except for IWM, QQQ, and SPY, which are always quoted in pennies.
The list of permitted classes doesn't seem to come from specific volume criteria. Instead, the SEC and the exchanges together roll-out names in phases.
CBOE's proposal for mini-options gives some additional insight:
There is a price test for entry into the Penny Pilot Program which excludes “high premium” classes, which are defined as classes priced at $200 per share or higher at the time of selection.
This is why GOOG is not in the Penny Pilot Program, for example.
The first 13 were some pretty active securities, but they definitely weren't the most.
chrisaycock's noted $3 threshold undoubtedly plays a role, so does volume, but there's probably some sort of other political consideration (like "don't leave out the small caps!") that could be quantified.
It looks like, generally speaking, it's the highest dollar volume underlyings with most option premium volume under $3 as well as a few political choices here and there.
Fun facts from the link:
I can't wait for the penny pilot to be over.