COVID-19 is causing serious impacts on tax revenue and consequentially on public health budgets. This study assesses Cambodia's public health services technical efficiency, unit costs, and utilization rates to quantify the extent to which current health financing can accommodate the expansion of social health protection coverage. Overall, for the public health system to be fully efficient output would need to increase by 34 and 73 percent for hospitals and health centers, respectively. We find public sector service quality, private sector providers, and non-discretionary financing to be statistically significant factors affecting technical efficiency. This study pioneers the application of Data Envelopment Analysis-Aumann-Shapley applied cost allocation to the health sector, enabling unit cost estimation for the major social health insurance payment categories. We estimate there is potential supply-side 'service space' to expand population coverage to an additional 4.69 million social health insurance beneficiaries with existing financing if the public health system were fully efficient.