In an attempt to develop an alternative process that meets the criteria of "green" and economically sound technology in fuel purification, simultaneous extractive desulfurization, denitrification, and dearomatization using natural deep eutectic solvents (NADESs) were investigated. A NADES composed of betaine (Bet) as a hydrogen bond acceptor (HBA) and levulinic acid (LevA) as a hydrogen bond donor (HBD) was investigated for its extraction capacity of thiophene, pyridine, and toluene from n-decane via liquid-liquid extraction. First, the HBA/HBD molar ratio was optimized based on the highest overall extraction efficiency, which was achieved for Bet/LevA (1:7). Furthermore, the selected NADES was characterized by measuring its density, dynamic viscosity, and water content. Then, the solubility of each fuel impurity in the NADES was measured. Moreover, the liquid-liquid equilibrium (LLE) data of the pseudo-ternary systems {n-decane (1) + thiophene/pyridine/toluene (2) + Bet/LevA (1:7) (3)} were determined at 298.15 K and 1.01 bar. The assumption of a pseudo-ternary system, which means that the NADES stays intact in one phase, was validated experimentally. The solute distribution ratios, selectivities, and the extraction efficiencies of each impurity at a 1:1 solvent-to-feed mass ratio were calculated from the experimental LLE data and compared to a benchmark solvent (i.e. sulfolane) and other ionic liquids and DESs reported in the literature. The LLE data were also correlated using the nonrandom two-liquid thermodynamic model. The regressed LLE data showed good agreement with the experimental data as the root-mean-square deviation was found to be <= 0.29%. Finally, it is clear that Bet/LevA (1:7) can be considered as a potential natural solvent for combined desulfurization, denitrification, and dearomatization processes.