What would be the most likely effect of one company buying a competitor?

The law mergers when the effect may be substantially to lessen competition or tend to create a monopoly. Three basic kinds of mergers may have this effect: Horizontal mergers, which involve two competitors; vertical mergers, which involve firms in a buyer - seller relationship; and potential competiton mergers, in which the buyer is likely to enter the market and become a potential competitor of the seller, or vice versa.