We present a high resolution study of the ferromagnetic layer thickness dependence of exchange bias field (H EB) and coercivity (H C) in IrMn/Co and FeMn/Co bilayers using the magneto-optical Kerr effect. Samples are sputtered wedges on silicon with Co thicknesses ranging from 1 to 17 nm. The IrMn/Co ͑with exchange bias interface energy of ϳ0.14 erg/cm 2 ͒ shows square loops, a smooth increase in H EB with inverse thickness, and a complicated behavior for coercivity, perhaps due to competition with thickness dependent coercive mechanisms. The FeMn/Co ͑with exchange bias interface energy of ϳ0.059 erg/cm 2 ͒ shows more rounded loops, a plateau of H EB with decreasing thickness, and a smooth increase in coercivity with inverse thickness.