The empirical formula is the simplest whole number ratio of atoms in a compound. To find the empirical formula, you need to find the greatest common factor of the subscripts in the molecular formula.

In this case, the greatest common factor of 12, 6, and 3 is 3. Dividing each subscript by 3 gives us:

C12H6O3 / 3 = C4H2O1

Therefore, the empirical formula for C12H6O3 is C4H2O.