Superparamagnetic colloid particles of iron oxides with typical dimensions of 50-100 nm in length and 10-15 nm in diameter have for the first time been detected in paraffin wax deposits withdrawn from a producing oil well. These particles occur in fractal aggregates of petroleum colloid particles. The results of the study formed the basis for the development of magnetic means of controlling the physicochemical properties of petroleum. The presence of iron oxide nanoparticles can lead to catalytic transformations of petroleum during its industrial processing. The composition of paraffin wax deposits was determined with the use of transmission electron microscopy in combination with the techniques of powder microdiffraction, characteristic electron-energy-loss spectroscopy, and electron magnetic resonance.