For petroleum and petrochemical enterprises, control and management of volatile organic compounds (VOCs) is a key link to achieving green and low-carbon development. As a major source of VOC emissions in the oil and gas industry, crude oil storage tanks have attracted significant attention with regard to reducing emissions. Based on continuous monitoring of breathing gas flow and VOCs concentration in crude oil storage tanks, this study systematically analyses the emission characteristics of VOCs-containing breathing gas from storage tanks of different types under different working conditions. The results show that the VOCs concentration in the breathing gas is significantly correlated with the storage tank's liquid level and temperature; the VOCs emission intensity in the breathing gas is negatively correlated with the storage tank's liquid level; the cumulative breathing gas volume in the storage tanks shows a good linear relationship with the liquid volume change in the storage tanks (R2 = 0.96); and the gas–liquid ratio of the test cases is in the range of 0.02–0.The composition of VOCs in breathing gas is significantly correlated with crude oil density, and an increase in crude oil density is significantly correlated with the density of crude oil. A significant correlation was observed between an increase in crude oil density and an increase in the content of heavy VOCs components in the breathing gas. The VOCs in the breathing gas of dilute oil were dominated by C2–C6 nonpolar alkanes, accounting for 74% of the total, while thick oil was dominated by C7–C12 nonpolar alkanes, accounting for 80% of the total. This study reveals the key emission laws of VOCs in the breathing gas of fixed-roof storage tanks, and its results can be used as an important basis for the daily operational control and management of VOCs in storage tanks.