In blank titration, the volume of HCl used is typically less than the volume of oil used. This is because the purpose of blank titration is to determine the concentration of the HCl solution, and a smaller volume of HCl is required to reach the equivalence point with a known volume of a weak base (such as NaOH) compared to the volume of oil required to reach the equivalence point with the same volume of HCl.

In oil titration, the volume of HCl used is typically much larger than the volume of oil used. This is because the purpose of oil titration is to determine the concentration of the oil sample, and a larger volume of HCl is required to react with all the base present in the oil sample compared to the volume of HCl required to reach the equivalence point with a known volume of a weak base.

In summary, the volume of HCl used for blank titration is less than the volume of oil used for oil titration due to the different purposes and requirements of each titration.