Why not simply express the size of the hep C market opportunity in terms of percentage of GDP? Huge numbers like these make investors excited, so it's no surprise to hep C drug stocks going ga-ga. Gilead Sciences' ( GILD) $11 billion purchase of Pharmasset helped, so did Bristol-Myers Squibb's ( BMY) $2.5 billion takeout of Inhibitex ( INHX). Meantime, analysts are touting these staggering estimates to justify valuations and price tags for hep C drug stocks. Idenix Pharmaceuticals ( IDIX) and Achillion Pharmaceuticals ( ACHN) are eyed as the next takeover targets. It looks like a hep C bubble to me but, then again, I'm a natural skeptic. Here's one way I look at the situation: Pharmasset, during its negotiations with Gilead, estimated that its hep C drugs could generate cumulative revenue of $91 billion. Compare that to cumulative sales of Pfizer's ( PFE) cholesterol drug Lipitor, which totaled about $120 billion before the pill went generic. It seems hard to believe that a hep C drug, or a combination of hep C drugs, could realistically generate revenue on par with the most successful branded commercial drug of all time. On paper it's possible, but in the real world? If the actual commercial opportunity for hep C drugs is smaller than what analysts and many investors believe it to be, then we are truly in the midst of a hep C bubble that will pop sooner or later. None of this means, by the way, that Idenix Pharmaceuticals can't be acquired for a huge premium. Illogical acts and irrational thinking define bubbles, so I wouldn't bet against a big drugmaker, desperate to be competitive in the hep C arms race, paying up to snag Idenix and its lead drug, the "nuc" IDX184. The same can be said for Achillion Pharmaceuticals, I suppose, although Achillion's lead protease inhibitor is more of a commodity these days. The company's NS5A inhibitor, further back in development, might generate more interest. If neither Idenix nor Achillion find buyers (which won't surprise me, either), the two companies could always merge. That might be the best idea, although speculative investors certainly hope for more. I also totally recognize that my skepticism may be overdone and that analysts and hep C drug companies are thinking clearly about the future of hep C revenue. I launched a discussion on this topic Wednesday night on Twitter. John LaMattina, a partner at PureTech Ventures and a former top executive at Pfizer (Twitter handle: @John_LaMattina) remarked that back in the day, Pfizer execs projected peak Lipitor sales of only $800 million to $900 million.