The triple differential cross section for electron impact ionization of the 3s orbital in argon has been measured in the coplanar asymmetric geometry, at a low incident energy of 113.5 eV (less than five times the binding energy) and ejected electron energies of 2, 5, 7.5 and 10 eV. Comparison of two distorted-wave Born approximation calculations with the experimental data reveals very poor agreement.