A magnetic device for treating oil flowing through crude oil supply lines is disclosed which is constructed of two concentric tubes with a series of tiers of magnetic means interposed in the annular space formed by the concentric tubing. The tiers are spaced one from another by spacers and connecting means are provided at each end of the concentric tubing to attach the device in an oil well supply tube string. All of the magnets in each tier have the same magnetic pole facing toward the tubing axis. The outer tubing is formed of a ferrous material and the inner tube is formed of a nonferrous metallic material such as copper.
