This experiment seeks to characterise the monolayer composition and structure of binary mixtures of fatty acid and amine. This represents a key additive system used commercially adsorbed at the iron oxide / oil interface. In particular, we aim to identify their interactions and any synergistic or competitive behaviour they exhibit, given that we have seen such behaviour in the bulk and when physisorbed on graphite. Only neutron reflection is able to provide the structural and compositional information required to underpin our understanding of these and related systems.