Silica catalyzes the tert-butyl hydroperoxide (TBHP, t-BuOOH) oxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-Me2DBT) to their oxides at 50-90 degrees C. Sulfur concentrations in simulated hydrotreated petroleum feedstock solutions containing 374 ppm of sulfur as DBT or 4,6-Me2DBT can be reduced to 1 ppm within 40 min at 90 degrees C. As an inexpensive, stable, and recyclable catalyst, silica has several advantages over other catalysts for the oxidation of DBTs to their easily separated oxides as a means of achieving low sulfur levels in petroleum feedstocks.