In this article we examine the institutional strategies and methods of biodiversity offset calculation employed by two mining companies in Madagascar. Much like the REDD+ mechanisms, these environmental projects are based on estimations of the past and predictions of the future, and require validation by international experts. They incorporate a set of standard indicators adapted to the affected habitats, and specially developed units of measurement to demonstrate ecological equivalence. The complex and diverse mitigation portfolios of these companies include aspects of both in-kind and financial compensation, and allow the combination of different types of programs that may be developed directly by the company or delegated to conservation non-governmental organizations (NGOs).