The libertarian position on economics is that private monopolies cannot exist in a true free market economy; antitrust laws are ineffective and since they represent government intrusion on private business, should not exist. Libertarian economics is based very often on the discussion of wealth and how it is created in Adam Smith's book Wealth of Nations, although the books is famous as being one that many people discuss, but few people have actually read. Adam Smith, in fact, devotes considerable discussion to monopolies, and the effects of them on pricing and the consumer.
Mises Institute website highlights statement about its leader, Murray Rothbard:
"Thus, for Rothbard there is no social 'problem' associated with monopoly in a free market."
Another page of the Mises Institute it defends exclusive contracts.
In this book featured by the Mises Institute, the author advocates the "total abolition of antitrust" laws.