The production of ultra-low sulfur and nitrogen containing diesel oil is gaining importance due to the strict limits set by government agencies. the sulfur content has to be limited to a maximum of 15 ppm and the nitrogen content to less than 0.1 ppm. the aliphatic sulfur and nitrogen compounds are highly reactive in conventional hydro-processing operations and can be completely removed from the fuels without much difficulty. however, the poly aromatic hydrocarbons or pah are difficult to reduce in hydro-treating processes. the poly-aromatic sulfur and nitrogen compounds, including alkyl indoles and alkyl carbazoles are generally more difficult to convert over hydro processing catalysts. therefore, the poly-aromatic compounds present the most difficult challenges to the hydrodesulphurization (hds) and hydrodenitrification (hdn) processes. further these pahs are the major source of pollution as it releases sox and nox to the atmosphere. this emission causes harmful effect to the environment and contributes to air pollution, greenhouse effect and acid rain. thus it becomes invariably necessary to extract the sulfur and nitrogen containing pah species from fuel oil by using physical methods at ambient condition. fuel oil is known to contain a small amount of nitrogen-based compounds (0.1% - 2% wt). the nitrogen content is also known to increase with increasing boiling point of the crude oil. they are also considered as strong inhibitors for the hydrodesulphurization process (hds) of diesel oil because of its role in catalytic deactivation. among the physical methods, the solvent extraction process is an imminent operation for removal of pahs both at ambient condition as well as moderate condition. the limitations of conventional solvents like sulfolane and n-methyl pyrrolidone (nmp) are well documented. the new generation green solvents such as ionic liquid (il) and deep eutectic solvents (des) have been used for extraction of pah and has hence gained immense importance. des are analogous to il and are also known as second generation ionic liquids which are considered as replacements for the more expensive ionic liquids. the formation of des at room temperature is due to the establishment of hydrogen bonds between the hydrogen bond acceptor (hba) such as an inorganic salt and a hydrogen bond donor (hbd) such as glycerol or ethylene glycol. des’s are also characterized by a very large depression of freezing point which makes them liquid at room temperatures. the freezing point depression of the mixture results from the formation of halide ion−hydrogen bond supramolecular complexes that alter the free energy of the solid phase compared to that of the liquid. in most cases, a des is obtained by mixing a hydrogen bond donor (hbd) that has the ability to form a complex with the halide anion of the quaternary ammonium or phosphonium salt. they are chemically inert and most of the synthesized dess are biodegradable, biocompatible, and nontoxic. in our work we shall focus our attention on the nitrogen containing pah such as quinolone and indoline. from our previous work it was found that the des with methyltriphenyl phosphonium bromide and ethylene glycol with a molar ratio of 1:4 respectively was found to be effective solvent for the removal of quinoline from heptane. however, a need is felt to study the simultaneous extraction of both toluene and pah component within the hydrocarbon stream. this is required since both the component co-exist together in diesel and can affect the selectivity and distribution ratios. to achieve such an objective, quaternary liquid liquid equilibrium data is required for the separation of quinoline and indoline from toluene – heptane mixture at temperature of 35 oc and atmospheric pressure. the distribution coefficient and selectivity can then be obtained to observe the simultaneous extraction performance with respect to the current chosen des. gibb’s free energy models such as nrtl and uniquac was then used to correlate the experimental data. further the multicomponent tie line data was also benchmarked and validated with the quantum chemical based cosmo-rs model.