Antitrust reverse termination fees (fee paid by the buyer to seller if the deal falls apart because of antitrust objections) are meant, in part, to compensate for the risk to the seller from an antitrust investigation, in addition to providing extra incentive to the buyer to get the deal done. These fees–in antitrust-sensitive deals–typically range about 3-4% of the purchase price.
In the internet industry, 20% may be the new 4%, reflecting the government’s keen interest/unpredictability in these acquisitions. Google’s Motorola Mobility acquisition has a $2.5 billion breakup fee, 20% of the $12.5 billion purchase price. Today, Facebook revealed that the Instagram acquisition has a $200 million breakup fee, again 20% of the $1 billion purchase price.