Background: Addressing inefficiencies in the way healthcare is financed has been identified as an important source of fiscal space for health systems. The WHO, for example, has argued that up to 40% of resources spent in health are wasted. Which reforms to focus on, their impact on fiscal space, and their feasibility have seldom been documented, however. The aim of this paper is to synthesise the evidence on these points, ascertaining the extent of fiscal space that has, to date, been created by implementing reforms aimed at addressing inefficiencies in health financing. Methods: systematic review of peer-reviewed literature in global databases (Medline, Embase, Global Health, Econlit, Africa-Wide information, Web of Science Core Collection and SciELO citation index). 20 articles were included for narrative analysis. Data extracted included: type of study; countries where the reform was implemented; the specific inefficiency discussed; the specific reform to tackle inefficiency; the efficiency indicator used; the baseline information given; the impact of the reform on health spending; and the feasibility and timing of the reform. Findings: Inefficiencies in health financing exist across the world, and reforms to address these remain important. Yet the empirical evidence on savings that can be created through addressing these inefficiencies is limited, mixed, and suggests that potential savings are more modest than indicated by the WHO. The feasibility of these reforms is seldom documented. The process of implementation of these reforms is similarly poorly documented, although the available evidence suggests that it takes three to ten years for these efficiency-enhancing health financing reforms to translate into actual results. Interpretation: Further research is needed to understand how to translate identified inefficiencies in the way healthcare is financed into additional fiscal space. Engaging with the political economy of designing and implementing these reforms will be key. Rooting fiscal space analysis projections in country-specific analysis of inefficiencies is also key, as the expectations of financial savings will otherwise be unrealistic.