Refinery off gases are treated in a plant in two processing steps, wherein the off gases are first scrubbed in a wash column using lean oils for removal of heavy mercaptans and C5+ hydrocarbons, and wherein a hydrotreater is then used for saturating olefinic hydrocarbons and reducing sulfurous compounds. Most preferably, lean recycle oil is used for temperature control of the hydrotreater reactor(s) in configurations where the lean oil from a hydrotreater reactor outlet separator is mixed with the reactor feed to so cool the hydrotreater reactor via evaporation.