Detailed characterization of oil sludge obtained from an electric dehydrator was performed using various analytical techniques and compared with that of its parent crude oil. The findings showed that the oil sludge was a stable emulsion consisting of oil, water, solids, and polyethers, which are chemical additives commonly used in the oilfield and refinery operations. Spectral peaks derived from positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) were assigned to sodium adducts [M + Na](+) for four types of polyethers that are nonionic surfactants. The Na1Ox class species found in the sludge at the bottom section of an electric dehydrator were likely due to their low solubility in oil as the number of oxygen atoms in these compounds increased. Polyethers were likely involved in the formation of oil sludge in the electric dehydrator. Sodium adducts, such as [M - 2H + Na](-) [M - 3H + 2Na](-), and [M - 4H + 3Na](-), of both C-80 and C60+ ARN acids found in the fractions derived from acidified toluene extraction of oil sludge solids ionized by negative-ion ESI were also identified that confirm the assignment of ARN acids.