Objective: High-pressure water mist fire suppression systems have been widely used for liquid fuel storage fire in China. In the event of a leakage and subsequent fire accident involving liquid fuels, the fire can rapidly spread owing to the heat feedback within confined spaces. High-pressure water mist fire suppression systems are favored for their energy efficiency, environmental protection, efficient cooling, and rapid smothering; however, their effectiveness in extinguishing liquid fuel fires requires further investigation. Methods: This study explored the impact of high-pressure water mist at different flow rates on fire suppression for different types of oil pool fires through full-scale experiments. An experimental platform was designed and built specifically for high-pressure water mist fire suppression in confined spaces, focusing on transformer oil and gasoline pool fires to investigate the extinguishing effects of water mist on these fires. Cold spray experiments were carried out to assess water mist flux using a measuring cup collection method, which provided crucial data for fire suppression tests. Simultaneously, fire extinguishing experiments were carried out, with thermocouples arranged near the experimental oil pools and on the walls to analyze variations in key parameters such as plume temperature, oil temperature, and wall temperature. Cameras were also installed to record the combustion process and flame morphology. Results: The experimental results indicate the following: (1) Under identical flow rates, high-pressure water mist is far more effective at extinguishing transformer oil pool fires than gasoline pool fires. For gasoline pool fires, the water mist can control the fire's spread within the confined space; however, even after five minutes of continuous application, complete extinguishment is not achieved. Despite a decrease in the burning area, flame height, and oil temperature, combustion continues. (2) Cold spray experiments reveal that water mist flux in the protected area increases directly with the flow rate of the high-pressure water mist. (3) The effectiveness of fire extinguishment is closely linked to the water mist flow rate. For transformer oil pool fires, higher water mist flow rates significantly shorten the extinguishment times. For gasoline pool fires, increased flow rates strengthen suppression effects but fell short of fully extinguishing the fire. (4) High-pressure water mist can provide continuous cooling to oil and surrounding walls, with cooling efficiency improving as water mist flow rate increases. Conclusions: The findings of this study provide valuable insights into the application of high-pressure water mist for fire suppression in confined spaces. This research offers important technical support for designing fire protection systems in critical areas of confined spaces, emphasizing the need to consider factors such as fuel type, water mist flow rate, and cooling efficiency.