An off gas extraction system cleans common sources of off gas, such as storage tanks and polluted soils. Off gas is extracted, followed by compression and condensation. Compression and condensation produce an off gas that can be reintroduced as a treated gas into the off gas source. Alternatively, a regenerative absorber cleans the treated gas by adsorbing residual chemical vapor and concentrates the removed chemical vapors and reprocesses them. If the treated gas is not reintroduced into the off gas source, conventional scrubbers may used on the back end of the system to produce a final exhaust as prescribed by environmental regulation. Methods of accomplishing the same are similarly provided, including novel methods for degassing storage tanks and treating polluted soils to meet current environmental regulations, as well as green technology and sustainability initiatives.