quality. Thus the results with and without regulator are the same of (19) and
(21).4
Proposition 1 In equilibrium only monopoly mergers occur with and without
MQS.
A merger involving the low-quality firm never occurs because firm 2’s strat-
egy of merging with the high-quality firm is strictly dominant. For the high-
quality firms (1 and 2) a bilateral merger under an MQS is more profitable than
a bilateral merger without regulation. Moreover, without regulation they prefer
a monopoly merger to a bilateral merger. Since no bilateral merger with firm 3
occurs, an MQS induces the low-quality firm to exit the market and leads to a
monopoly. Thus in equilibrium the monopolization of the market occurs with
or without a MQS.
4 Conclusions
When endogenous mergers are allowed, if a welfare maximization regulator
chooses an MQS as in Ecchia and Lambertini (1997) in Scarpa’s (1998) model,
then the market ends up being monopolized and the lowest quality firm exits.
4Our results confirm Scarpa (1998) in the matter of the relation between the efficient
number of firms and the lowest quality.