While it's common that shares of a company receiving a merger or takeover offer often jump when the news is announced, some surges recently have been extreme.

During the third quarter, takeover offers for companies were made at prices 41% higher, on average, than the shares of the targeted companies traded at a week before the acquisition offers were made.

Deal prices aren't normally this far above where stocks trade just before a buyout offer, Dealogic says: The difference is historically closer to 32%. This year so far, the difference is 38.2%, the highest since 2001. Analysts say takeover bids may be high relative to stock prices because of:

Stubborn sellers unwilling to accept market values. Companies are willing to entertain buyout offers, but see current stock prices as still too low to be reasonable, says Morton Pierce, head of mergers and acquisitions for law firm Dewey & LeBoeuf. In fact, in the first quarter, when the market was even lower, the gaps between stock prices a week before deals and takeover bids were wider than in the third quarter.

Competition for deals heating up. M&A activity is no longer in free fall, which brings more players. This year, there have been 5,851 deals for U.S. firms worth $636 billion. That's down from last year, but activity is stabilizing, Dealogic says. Buyers fear they must make serious offers or another company may beat them, says Jeffrey Stein of law firm WilmerHale.