This paper focuses on the role of public environmental agencies in market-based conservation. It compares two contrasting cases of a common market-based conservation instrument, 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 morphology reveals how they differ by size, organizational configuration, regulatory pressure, type of metric and robustness. Despite common regulatory framework and objectives, these two instruments essentially differ on the type of constitutive agreement: private single conservation banks, as small confined over-the-counter economic exchanges, are based on an agreement on exchange with less attention on metrics and credit definition. Habitat exchanges are wider inclusive centralized marketplaces within which agreement is settled on metric and credit harmonization. The reliance on distinct metrics establishes varying forms of public accountability within the instruments and questions the need to regulate metrological processes.