A natural monopoly is when one firm has the ability to supply the entire market at lower prices than two or more firms. A natural monopoly faces downward-sloping average cost (AC) for the entire range for which demand is applicable. The reason for its downward-sloping AC curve is usually that the initial investment in the infrastructure of the firm is large, but once it is in place, the marginal cost (MC) of production is low, for example hydro power. This high establishment cost is a strong barrier to entry and a natural monopoly could undercut any would-be competitor so they could not survive. Natural monopolies often involve some kind of network, for example water, gas,phone, rail.
Equilibrium Output-Natural Monopoly
The rule for maximising profit or minimising a loss (the equlibrium) for a natural monopoly is the same as any other firm. The most profitable output or smallest loss is where marginal revenue (MR) equals marginal cost (MC). Any other position will result in a smaller profit or greater loss. Therefore, the equilibrium output is at a price of Pe and quantity Qe (determined from the intersection of the marginal cost and marginal revenue curves). At the equilibrium output Qe the natural monopoly is making a supernormal profit (of $100m) and produces less than what society or consumers desire. Operating at the equilibrium output position creates a deadweight loss of BFG because consumer surplus and producer surplus are not maximised. The natural monopoly is charging a price in excess of marginal cost (P > MC), this is called mark-up pricing. At the equilibrium output in perfect competition, price and marginal cost are the same. Sellers cannot charge higher prices because they would immediately lose sales to competitors. This is called marginal cost pricing and occurs in perfect competition where at the equilibrium output position price equals marginal cost (P = MC).
A natural monopoly charges more and produces less than would be the case if the firm operated as a perfect competitor. Overpricing and not operating at the allocatively efficient (socially optimum) level means that a natural monopoly can be seen as socially undesirable. However, if consumers are not subject to competitive advertising and marketing, they receive the good or service at cost and the firm carries out R & D (research and development) a natural monopoly can be viewed as socially desirable. A natural monopoly may also be seen as socially desirable because it is wasteful to duplicate the existing infrastructure, so encouraging competition is seen as undesirable. If output is below equilibrium Qe (where MR equals MC), the firm would be missing out on marginal profits because the revenue from producing the last article is greater than its cost of production, implying that the firm could increase output and increase profit. However, increasing output beyond Qe reverses the position. The firm will be making marginal losses because the revenue from one additional article is now less than the cost of its production.
If increased output adds more to cost than to revenue, a firm has obviously passed the point of maximum profit (or minimum loss). Price discrimination may be practised by any monopolist. This is where they segment the market in some way, for example domestic and industrial users may be charged at different rates. A two-part tariff is a system where users are charged a fixed amount for a given time period and per unit charge for use, for example with the phone there is a line rental and a charge for toll calls. Off-peak pricing is a system of charging that results in a higher price at peak time usage than at off-peak times, for example toll calls made after 6 p.m. are at a cheaper rate.