You need to have some significant market power (yes, vague) such that your elasticity of demand is steep and elasticity of supply of competitors is steep. That

You need to have some significant market power (yes, vague) such that your elasticity of demand is steep and elasticity of supply of competitors is steep. That is not a requirement for antitrust law. That is just some silly threshold the Justice Department set for itself so that it wouldn't have to do its job. Until the [EDIT: Clinton] administration, businesses were successfully charged with antitrust violations even though in many cases they were minor market participants on the basis of their actions resulting in anti-competitive effects. (Usually as a result of price-fixing agreements between smaller participants.) After the Microsoft case, the DOJ decided to bring "economic analysis" into the mix to "improve" their antitrust practice, and it resulted in the DOJ not pursuing any meaningful antitrust cases at all, on the grounds that basically everything was kosher if you looked at it from a sufficiently macroeconomic perspective. (This also overlapped with the Dubya administration, and there was strong political pressure not to go after American companies.) Interestingly enough, Apple was the last major antitrust case that the DOJ successfully pursued. (That case involved Apple arranging a price-fixing arrangement for ebooks.)