Oligopolistic competitionLinks to an external site. can give rise to both wide-ranging and diverse outcomes. In some situations, particular companies may employ restrictive trade practices (collusionLinks to an external site., market sharing etc.) in order to inflate prices and restrict production in much the same way that a monopolyLinks to an external site. does. Whenever there is a formal agreement for such collusion, between companies that usually compete with one another, this practice is known as a cartelLinks to an external site.. A prime example of such a cartel is OPECLinks to an external site., which has a profound influence on the international price of oil. Firms often collude in an attempt to stabilize unstable markets, so as to reduce the risks inherent in these markets for investment and product development.[citation neededLinks to an external site.] There are legal restrictions on such collusion in most countries. There does not have to be a formal agreement for collusion to take place (although for the act to be illegal there must be actual communication between companies)-for example, in some industries there may be an acknowledged market leader which informally sets prices to which other producers respond, known as price leadershipLinks to an external site.. In other situations, competition between sellers in an oligopoly can be fierce, with relatively low prices and high production. This could lead to an efficient outcome approaching perfect competitionL