A task-specific ionic liquid, 1-pentyl-3-methylimidazolium peroxydisulfate (PDS) with a chemical formula of [C(5)mim](2)[S2O8], was synthesized in the present study and used as an oxidant in the extractive and catalytic oxidative desulfurization (ECODS) process. Another ionic liquid, [C(5)mimCl][CoCl2], was used as a catalyst/extractant coupled with the PDS oxidant. The developed ECODS system showed excellent desulfurization performance under relatively mild conditions, with a sulfur removal of 98.7% observed under the following conditions: 6 g of model oil (500 ppm), 1.5 g of [C(5)mimCl][CoCl2], and 0.5 g of [C-5-mim](2)[S2O8]; temperature = 30 degrees C; time = 65 min. For model oil with an initial sulfur content of 250 and 1000 ppm, sulfur removal of up to 99.1 and 96.9% was achieved, respectively. The reactivity of the three sulfur substrates followed the trend of DBT > BT > 4,6-DMDBT. In addition, the ionic liquid oxidant was proven to also function as an extractant. The tuning of the cation of the PDS salt from inorganic potassium to 1-pentyl-3-methylimidazolium lowered the activation condition efficiently, proving another way for the activation of PDS.