Project management literature has, until now, mainly focused on new build and only in the last decades the issues of decommissioning (mega) projects has arisen. To respond to this changing environment, project management will need to understand the challenges of decommissioning projects. Decommissioning projects within Oil & Gas, Chemical and Nuclear sectors are characterized by high costs, long schedules and uncertainty-based risks. The budget for Nuclear Decommissioning Projects and Programmes (NDPs) are subject to well publicized increases and, due to their relatively recent emergence, complexity and variety, key stakeholders lack a full understanding of the key factors influencing these increases.
Benchmarking involves “comparing actual or planned practices [...] to identify best practices, generate ideas for improvement”  and offers significant potential to improve the performance of project selection, planning and delivery. However, even if benchmarking is the envisaged methodology to investigate the NDPs characteristics that impact on the NDPs performance, until now, it has only been partially used and there is a huge gap in the literature concerning benchmarking NDPs.
This paper adapts a top-down benchmarking approach to highlight the NDPs characteristics that mostly impact on the NDPs performance. This is exemplified by a systematic quantitative and qualitative cross-comparison of two major “similar-but-different” NDPs: Rocky Flats (US) and Sellafield (UK). Main results concern the understanding of the alternatives of the owner and/or the contractors in relation to (1) the physical characteristics and the end state of the nuclear site, (2) the governance, funding & contracting schemes, and (3) the stakeholders’ engagement.