Reported experimental trends in charge carrier tuning in single molecule junctions of oligothiophene-based wires are rationalized by means of frontier molecular orbital theory. The length and substituent effects on the frontier orbitals energy levels’ are shown to translate to the computed transmission spectra – with a caveat of the role of the linker group. The resulting transport (charge carrier) type – n- (electrons) or p- (holes) – is easily identifiable from the in silico charge transfer trends.