We consider the pricing of a uniformly mixed pollutant when enforcement is costly with a model of optimal, possibly firm-specific, emissions taxes and their enforcement. We argue that optimality requires an enforcement strategy that induces full compliance by every firm. This holds whether or not regulators have complete information about firms’ abatement costs, the costs of monitoring them for compliance, or the costs of collecting penalties from noncompliant firms. Moreover, ignoring several unrealistic special cases, optimality requires discriminatory emissions taxes except when regulators are unable to observe firms’ abatement costs, the costs of monitoring individual firms, or any firm-specific characteristic that is known to be jointly distributed... |