Herding agents offer a significant advance in oil spill response by overcoming past barriers limiting effectiveness of in-situ burning. This paper reviews the use, environmental fate and effects of two commercial herders, Siltech OP-40 and ThickSlick 6535. A conceptual model is proposed to describe herder fate followed by a screening exposure analysis. Hazard concentrations intended to protect aquatic life are derived using empirical toxicity data, interspecies correlation estimation and group target site models. Using exposure and hazard evaluations, a preliminary risk assessment is performed demonstrating acceptable risk to aquatic life. Hazards posed to wildlife are also reviewed. Potential harm to wildlife can be avoided or minimized by adopting best management application practices. This synthesis is intended to provide a valuable resource describing the rationale for herder use, evaluating environmental risk trade-offs and informing future oil spill response planning and decision-making. Priorities for further research are identified.