When positive externalities exist in the consumption of a good, the marginal social benefit: Multiple Choice could be either greater than or less than the marginal benefit received by consumers of the good depending on the equilibrium price determined in competitive markets. equals the marginal benefit received by consumers of the good minus the marginal benefit to third parties. equals the marginal cost of producing the good plus the marginal cost to third parties. equals the marginal benefit received by consumers of the good plus the marginal benefit to third parties.