This article compares two contrasting cases of a widely used market-based conservation policy, namely private single conservation banks and habitat exchanges as two economic mechanisms for the production and circulation of species credits. The analysis of their economic morphologies reveals differences regarding regulatory pressure, organizational configuration, type of metric and robustness. Despite common objectives, these two policy instruments essentially differ in terms of the type of constitutive agreement they employ: private single conservation banks, as local and confined economic exchanges, are based on an agreement about exchange with little attention to metrics and credit definition. Habitat exchanges on the other hand tend to be wider and inclusive centralized marketplaces within which agreement is settled in terms of metric and credit harmonization. The reliance on distinct metrics establishes varying forms of accountability within these policy instruments and raises questions about the need to regulate metrological processes.