The effect of a magnetic field on the structural and rheological properties of crude oils with various concentrations of resins, asphaltenes, and paraffin hydrocarbons was examined. It was found that magnetic treatment leads to substantial changes in the paramagnetic, antioxidant, and viscosity characteristics of paraffin-base and high-viscosity oils. A factor that characterizes the quantity of inhibition centers increases with an increase in the amount of alcohol-benzene-extractable resins in the oils. The time of complete recovery of paramagnetic and antioxidant properties coincides with the recovery time of the rheological characteristics of petroleum.