There is diverging empirical evidence on the competitive effects of horizontal mergers: consumer prices (and thus presumably competitors' profits) often rise while competitors' share prices fall. Our model of endogenous mergers provides a possible reconciliation. It is demonstrated that...

A government wanting to promote an efficient allocation of resources as measured by the total surplus, should strategically delegate to its competition authority a welfare standard with a bias in favour of consumers. A consumer bias means that some welfare increasing mergers will be blocked....

Anticompetitive mergers increase competitors' profits, since they reduce competition. Using a model of endogenous mergers, we show that such mergers nevertheless may reduce the competitors' share-prices. Thus, event-studies can not detect anti-competitive mergers.