The regulator of a natural monopoly that sets a two-part tariff and whose marginal cost is stochastic will generally want the price to vary less than marginal cost when the lump-sum charge in the tariff is fixed. A trade-off exists between efficient pricing and an optimal allocation of risk....

The paper shows how commodity taxes can provide insurance to consumers when the producer price is volatile. Specific and ad valorem taxes have differing roles. The optimal specific tax is positive when demand has some elasticity. The optimal ad valorem rate is zero when demand is unit-elastic,...