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Oil storage tanks also require oil and gas recovery systems, as they are another significant source of oil and gas emissions; therefore, it is necessary to install such recovery systems in oil storage tanks as well. The oil recovery system for storage tanks differs from that used in gas stations; the recovery process is carried out in three stages: during oil unloading, when there is no oil stored, and during oil dispensing. It is uncertain which method will be used for recovery; there are many different approaches to recovery systems, and we can take a look at the specific ones. The oil and vapor recovery system for oil storage tanks needs to capture all the oil and vapor that evaporate at each stage. Generally, oil vaporization occurs in three stages: minor breathing, major breathing, and oil emission, and each of these stages is an important stage for recovery. The oil and vapor recovery systems on tank trucks use three recovery methods: adsorption, condensation, and membrane separation. The adsorption method used in oil storage tank recovery devices involves passing the gas-oil mixture through a liquid separation tank to remove any condensate carried therein, after which the mixture enters carbon beds that are in an adsorption state (with two carbon beds working alternately). The hydrocarbon gases are absorbed by the activated carbon, and the purified gas is released into the atmosphere. The adsorbed saturated carbon bed is subjected to vacuum desorption, and then converted into liquid gasoline through absorption or other methods, thereby achieving oil and gas recovery. Since the activated carbon needs to be replaced frequently, and several tons are required for each replacement, the operating costs are high; it is therefore more suitable for enterprises with high oil production volumes. The condensation method for oil storage tank recovery utilizes the difference in vapor pressures of hydrocarbons at different temperatures; by gradually cooling the mixture within an appropriate temperature range, the vapor pressure of most of the released oil and gas is brought to a supersaturated state, thereby causing the supersaturated oil and gas to condense and form liquid gasoline as a means of recovering such oil and gas. The downside is that the lower the cooling temperature, the higher the recovery rate of gasoline vapor, but a large amount of energy is consumed in the cooling process. The membrane separation method used in oil storage tank recovery systems represents a relatively new technology for oil and gas recovery. The hydrocarbon-containing gas is pressurized and then sent to a membrane separator; on the selective membranes used in such systems, oil and gas have a higher ability to penetrate compared to air. As a result, the hydrocarbon-containing gas is separated into two streams: an oil-rich stream and an oil-poor stream. The oil-rich stream has its hydrocarbons absorbed back by the oil product, while the residue with low oil content is reprocessed to meet the required standards before being released as purified gas. The investment costs for the adsorption and condensation methods are roughly comparable; however, within reasonable levels of investment and energy consumption, the condensation method can easily meet emission standards of less than 10 g/m3, whereas the investment and operating costs will increase significantly. The adsorption method finds it difficult to meet emission standards below 25 g/m3, and it also poses safety risks. Every recovery process has its own advantages and disadvantages. Oil storage tanks take advantage of the strengths of several recovery processes, allowing their respective advantages and disadvantages to complement each other and thus enhancing the functionality of the recovery system.