This research investigates alteration in the composition of diesel and engine oil due to their treatment with 35g of Potassium Aluminium Sulphate, (KAl(SO4)2) for seven days at room temperature. Results reveal that after treatment, the Total Petroleum Hydrocarbon (TPH) of diesel increased from 7688.38mg/l to 12505.10mg/l whereas that of engine oil increased from 4967.48mg/l to 7700.47mg/l. This suggests that within these seven days, the salt was able to alter the composition of the samples by breaking down higher molecular weight hydrocarbon fractions within and above the C40 range to smaller molecular weight fractions within the C6 to C40 range. The TPH of the treated diesel oil was similar to that of kerosene after treatment and that of the treated engine oil was similar to that of the untreated diesel sample. Ratios calculated from fingerprints of the samples such as nC20/nC24, nC18/nC24, nC18/nC20, nC7/nC9, and ∑K/∑D for the treated diesel sample (0.76, 0.57, 0.75, 0.16, and 0.84) respectively were slightly similar to that of kerosene (0.65, 0.79, 1.20, 0.5, and 1.08), but different from that of the untreated sample whereas ratios like nC10/nC11, nC11/nC12, nC14/nC16, nC11/nC20 and nC24/nC28 for the treated diesel sample (0.53, 0.35, 1.02, 0.67 and 4.44) were similar to that of the untreated diesel sample (0.52, 0.36, 0.92, 0.46 and 5.47). None of the ratios for the treated engine oil sample were similar to either those of the untreated engine oil sample or those of diesel. Therefore, though the treatment of the samples with 35g of the salt caused alterations in the chemical composition of the samples, it did not totally transform them to the fraction obtained before them during distillation process.