Increasing overall fiscal space is important for the health sector due to the centrality of public financing to make progress towards universal health coverage. One strategy is to mobilize additional government revenues through new taxes or increased tax rates on goods and services. We illustrate how countries can assess the feasibility and quantitative potential of different revenue-raising mechanisms. We review and synthesize the processes and results from country assessments in Benin, Mali, Mozambique and Togo. The studies analysed new taxes or increased taxes on airplane tickets, phone calls, alcoholic drinks, tourism services, financial transactions, lottery tickets, vehicles and the extractive industries. Study teams in each country assessed the feasibility of new revenue-raising mechanisms using six qualitative criteria. The quantitative potential of these mechanisms was estimated by defining different scenarios and setting assumptions. Consultations with stakeholders at the start of the process served to select the revenue-raising mechanisms to study and later to discuss findings and options. Exploring feasibility was essential, as this helped rule out options that appeared promising from the quantitative assessment. Stakeholders rated stability and sustainability positive for most mechanisms, but political feasibility was a key issue throughout. The estimated additional revenues through new revenue-raising mechanisms ranged from 0.47-1.62% as a share of general government expenditure in the four countries. Overall, the revenue raised through these mechanisms was small. Countries are advised to consider multiple strategies to expand fiscal space for health.