Purpose – This paper aims to understand the factors that influence a supplier’s choice to treat selected customers more preferentially than others. Suppliers often lack the resources to treat all their customers equally, instead having to make choices to treat some customers as preferred. Empirical evidence indicates that preferential treatment by suppliers provides substantial benefits for the purchasing firm. Design/methodology/approach – This study applies a mixed-methods approach. First, a qualitative analysis of a sample of buyers from an automotive manufacturer was conducted. In the second step, the findings were triangulated via a quantitative survey among key account managers of the automotive firm’s suppliers. Findings – This paper is the first to provide quantitative data collected from a large sample of automotive suppliers about the drivers of preferential customer treatment. The authors were able to show that the growth opportunities for suppliers and customers’ operative excellence, reliability and relational behavior are factors that induce suppliers to award preferential customer treatment. In contrast, innovation potential for suppliers, customers’ support of suppliers, supplier involvement and contact accessibility do not show a significant effect on suppliers’ behavioral intentions toward preferential customer treatment. Originality/value – The mixed-methods approach is introduced as a form of academic enquiry in supply chain management. The factors influencing preferential customer treatment by suppliers are explored in discussions with purchasers and validated in a subsequent survey among suppliers. Recommendations for managerial practice and theory are drawn.