[yardie]

During an acquisition the price on the shares of the acquirer goes down while the acquiree goes up. Since most mergers tend to be stock swaps rather than cash they would have to invest more shares than originally intended. If the merger falls through both would lose out as the acquirer would be seen as wasting a lot of money with nothing to show and the acquiree would be see as not so valuable.

[dllthomas]

They could still, in principle, negotiate around fixed numbers of shares instead of market values.

[saryant]

XOM initiated a very aggressive share buyback program ~15 years ago, their own treasury is one of their largest shareholders.

Makes much more sense for them to use those shares in acquisitions in the form of a stock swap.