Biodiversity offsets are commonly used to compensate for unavoidable development impacts on species or ecosystems by creating a benefit for the same species or ecosystem elsewhere. For offsets to work as intended, we need to be able to quantify how much benefit an offset action will provide for a species or ecosystem, so that we can make sure that the offset completely compensates for the development impact. For many poorly-understood species and ecological communities, however, important knowledge gaps exist making it hard to know what type of, and how much, offset action is needed to offset a given impact. This project developed an approach for eliciting the knowledge of threatened species experts in a structured way, so as to guide estimates of the benefits of alternative offset approaches. We tested the approach using several case study species that commonly trigger offset requirements, and for which developing appropriate offset proposals is considered challenging. Here, we describe the approach and findings for a suite of threatened reptiles that occur in the Brigalow Belt bioregion of eastern Australia.