None is illegal if you don't have a monopoly.

WalterBright · on March 7, 2016

So if you do have a monopoly, what is the legal price to charge?

dhimes · on March 7, 2016

The monopoly is what is illegal, not the price you charge.

robotresearcher · on March 7, 2016

It's not illegal to have a monopoly. It's illegal to exploit it in certain ways.

dhimes · on March 8, 2016

This is mostly a distinction without a difference in practice. Exploit it in certain ways and your monopoly gets broken apart- thus illegal. See ATT/ Ma Bell

robotresearcher · on March 9, 2016

It's a very practical distinction since you can avoid exploiting it in certain ways and thus not get into any trouble at all. Violator monopolies do not exert predatory pricing, etc, by accident.

dhimes · on March 9, 2016

Very good point.