Viability connotes a system’s ability to become ultra-stable through effective self-regulation of its internal processes and information processing among its subsystems. Applying this to an infrastructure delivery system (IDS) context, this study proposes that an IDS can successfully deliver on client requirements only if they attain and maintain viability. Research into the influence of National Culture (NC) on an IDS’s viability appears to be lacking; hence this study. Adopting a multi-case study, qualitative research design, this study explores three IDSs involved in the delivery of infrastructure projects in two different NC contexts; Nigeria and the United Kingdom. 25 semi-structured interviews were conducted across the cases to provide for an in-depth understanding of existing interactions between participants in these delivery systems: client/project sponsor; main contractor and subcontractors and to understand the influence of the prevailing national culture on such interactions, if any. Findings indicate that NC in project delivery environments influence the ability of IDSs to attain viability, especially as it pertains to the sustenance of Team Quality Attributes (TWQ) within the system. Based on these findings, it is expected that in modelling IDSs for viability, adequate consideration should be given to the prevailing NC by project managers and planners.