Vapor (or vapour) recovery is the process of recovering the vapors of gasoline or other fuels, so that they do not escape into the atmosphere. This is often done (or required by law) at filling stations, in order to reduce noxious and potentially explosive fumes and pollution.
The negative pressure created in the (underground) tank by the withdrawal is usually used to pull in the vapors. They are drawn-in through holes in the side of the nozzle and travel through special hoses which have a return path.
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Vapor recovery is also used in the chemical process industry to remove and recover vapors from storage tanks. The vapors are usually either environmentally hazardous, or valuable to be recovered. The process consists of a closed venting system from the storage tank ullage space to a vapor recovery unit (VRU) which will recover the vapors for return to the process or destroy them, usually by oxidation.
Vapor recovery units are also becoming commonly used in the oil and gas industry as a means of recovering natural gas vapor and making it a usable and profitable product. Specifically a newer form of vapor recovery technology, Ejector Vapor Recovery Units create a closed loop system which not only recovers valuable vapor, but also reduces methane and VOC emissions. 
Vapor Recovery Towers are also used in the oil and gas industry to provide flash gas recovery at near atmospheric pressure without the potential of oxygen ingress from the top of the storage tanks. The ability to create the vapor flash inside the Vapor Recovery Tower often reduces storage tank emissions to less than 6 tons per year, exempting the tank battery from Quad O reporting requirements.