We evaluated the traceability of mammalian records reported in the framework of environmental licensing in the oil sector in Colombia based on a sample of 43 projects licensed during 2014. Our analysis was done using the method we have proposed based on the concept of biological voucher. Our results showed a lack of the verifiable biological evidence that allows to test or review the identity and features of reported mammals. Under these circumstances, the information loses reliability and its eventual use, review or reinterpretation in future research work is restricted. If this condition proves to be a common feature in the studies of fauna presented for projects licensing, it would imply that a unique opportunity to increase the knowledge on the country’s biological diversity is being wasted, and that decision-making on environmental viability of oil projects is supported on mammalian studies with a significant degree of uncertainty in terms of the identity and characteristics of the recorded taxa. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat.