<p>This work presents new Liquid–Liquid Equilibrium (LLE) data for the extraction of thiophene from long-chain <i>n</i>-paraffins (<i>n</i>-dodecane, <i>n</i>-tetradecane, and <i>n</i>-hexadecane) using a homologous series of ionic liquids (IL), namely 1-pentyl-3-methylimidazolium hexafluorophosphate [C₅mim][PF₆], 1-hexyl-3-methylimidazolium hexafluorophosphate [C₆mim][PF₆], and 1-heptyl-3-methylimidazolium hexafluorophosphate [C₇mim][PF₆], at 313.15 K and atmospheric pressure. The study addresses the lack of systematic thermodynamic equilibrium data for intermediate alkyl chain lengths and provides insights into structure–property relationships governing the extractive desulfurization process. Experimental tie-line compositions were determined, and distribution coefficient (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(K\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>K</mi> </math></EquationSource> </InlineEquation>) and selectivity (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(S\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>S</mi> </math></EquationSource> </InlineEquation>) values were evaluated to assess extraction performance. The results indicate strong preferential partitioning of thiophene into the IL phase, where the extraction performance dependent on both the paraffin chain length and the IL structure. Distribution coefficients increase with increasing paraffin molecular weight, reflecting reduced hydrocarbon solubility in the IL phase, while the decrease in the distribution coefficient with increasing thiophene concentration is attributed to saturation of specific solute–solvent interactions (<i>K</i>=3.03–4.87, <i>S</i>=548–946). Among the investigated ILs, [C₅mim][PF₆] exhibited superior extraction performance, attributed to an optimal balance between polarity, viscosity, and molecular interaction strength. The experimental data were successfully correlated using the non-random two-liquid (NRTL) model, yielding an average root-mean-squared-deviation (<i>RMSD</i>) of 0.136. The stability of the ILs was ensured under controlled low-moisture conditions, minimizing hydrolysis of the [PF₆]⁻ anion. The generated dataset provides valuable thermodynamic information for the design of ionic liquid-based separation processes and contributes to a deeper understanding of the role of IL structure in extractive desulfurization.</p>