This document specifies a method for the determination of the oxygen content in bio-based products using an elemental analyser. The scope is limited to products containing elements C, H, O, N, Cl, Br and I without F, representing at least 95 % of the composition of the product to be analysed. NOTE 1 Bio-based materials can contain inorganic components. Oxygen in these inorganic components is not bio-based but will nevertheless contribute to the amount of oxygen determined by the following prescribed methods and therefore influence the results in terms of oxygen content. NOTE 2 Although this document has been drafted for the purpose of the determinations dealing with bio-based content, it can be also used as a standalone standard for determination of oxygen in organic compounds. NOTE 3 For the purposes of this document, the term % (m/m) is used to represent the mass (¼) of a material.