A time domain analysis procedure is used to calculate maximum design tensions for the mooring system of a truss spar. Fairlead motions are used as input to calculate time histories of dynamic mooring line tensions. Several random simulations are used to derive design values of maximum tension. The variability from simulation to simulation in maximum tension and in the dynamic portion of the response is summarized. Alternative methods for estimating the maximum value are compared and the effect of the number of simulations on the uncertainty in the maximum is demonstrated. The dynamic characteristics of the mooring line tensions are examined by looking at the high frequency and low-frequency portions of the response. A comparison of mooring line tensions for a truss spar and a classic spar is also provided. In addition, maximum tensions from the time domain analysis are compared with results from a frequency domain analysis.