A gain profile calculated using spectroscopic data for an XeCl excimer is shown and discussed. A numerical study of coherent amplification of ultrashort pulses in an XeCl gain medium is described. The real structure of the vibrational-rotational gain spectrum is generated by the model, and 100 transitions in each of the P and R branches for six different vibrational transitions are considered using the Maxwell-Bloch equations. This model can successfully predict coherent effects caused by multiquantum transitions. Calculated gains and pulse widths (FWHM) of the amplified pulses as a function of small signal gain-length products and the changes in the pulse shape are shown, assuming a 350-fs Gaussian input laser pulse at a total energy of 10 μJ/cm2. The saturation of amplified energy is caused by the formation of an effective 2π pulse.