This exploratory site-centred research investigates barriers to internal supply chain integration in practice, using systems thinking. A multi-method procedure termed the Quick Scan Audit Methodology is applied to four engineering to order case companies from two different country settings to identify and categorize the actual barriers to internal supply chain integration. The study establishes that the case-significant barriers to internal supply chain integration chiefly relate to behavioral / cultural factors and the organizational arrangement / structures imposed on employees. A cross-case comparison reveals two major clusters of supply chain integration barriers termed “fire-fighting” and “functional-silo mentalities”. The fundamental structures of these clusters are identified.