If a negative externality exists for sales of gasoline in a competitive market, more than the efficient amount of gasoline will be sold per year. The marginal social cost is higher than the marginal private cost, therefore too much is produced. In a Lindahl equilibrium, each consumer of a pure public good consumes the same quantity and pays a tax-share per unit of the good equal to his or her marginal benefit. A Lindahl equilibrium provides the efficient quantity of the public good. Because it is a public good all consumers have to consume the same quantity.
Efficiency requires that the sum of the marginal benefits for all consumers equal the marginal cost.
In addition, the consumers are happy with this scheme because all of them equate marginal private benefit to marginal private cost. If all voters have single-peaked preferences, a political equilibrium will not be possible under majority rule. Single peakedness over one issue is a condition that guarantees that under majority rule the median voter's most preferred outcome is the winner.