As an important intermediary between upstream refineries and downstream urban gas stations, volatile organic compound (VOC) emissions from urban oil depots were often disregarded, underestimating their environmental and health implications. An extensive investigation of urban depots' fuel composition and operational dynamics was conducted nationwide. We developed a novel approach that integrates theoretical models with easily measurable operational data from the depots to evaluate the efficiency of post-treatment devices in actual situations. Even in well-managed oil depots, the actual control efficiency of vapor recovery units fluctuates between 63% and 85%, depending on the concentration of hydrocarbon vapors in the intake of the device. The national emission factors for gasoline, diesel, and aviation kerosene at a national level were 6.64±1.16, 2.07±0.42, and 6.17±1.05 tons per 10,000 tons, respectively. In 2019, China's urban oil depots emitted 165 thousand tons of VOC. Enhancing control strategies by optimizing the physical and chemical parameters of refined oil, improving storage capacity and turnover efficiency, and upgrading storage tanks had the potential to reduce emissions by more than 60%. However, a 30% failure rate in these systems could negate the benefits of these improved strategies. Environmental implicationVOCs are recognized pollutants whose emissions and secondary products adversely affect the environment and human health. Due to the proximity of urban storage facilities to cities and the often-overlooked emissions from these facilities, their impact on the environment and health is underestimated. This study introduces a novel method to effectively evaluate the control efficiency of post-treatment devices at oil storage facilities under actual operating conditions. As a result, the national average VOCs emission factor for refined oil was calculated to be 4.33±0.99 tons per ten thousand tons, with total emissions exceeding 160,000 tons. This method can be used to accurately assess VOC emissions from urban storage facilities, highlighting the critical need for data-driven control strategies to improve emission management efficiency.