The 2004–2008 hurricane season in the Gulf of Mexico (GOM) saw several exceedances of what was regarded, prior to that period, as the 100-year significant wave heights (SWHs) that are used for the design of offshore oil and gas facilities. As a result, these facilities sustained considerable damage and disrupted U.S. energy supplies. The wave climatology in the GOM is therefore studied in detail. A 51-year database of SWHs was constructed by using a combination of wind and wave models, and both individual wave heights and statistical measures were validated, to the extent possible, using buoy data. Analyses of the modeled data show that there is an increasing trend in the annual maximum SWHs in the eastern part of the GOM; the maximum trend is approximately 5.6 cm/year, which is of the same magnitude as that reported for the U.S. west coast. The western part; on the other hand, shows a decreasing trend. The maximum estimated 100-year SWHs (denoted by SWH100) are 19.1 m, 22.6 m and 26.7 m for the Gumbel, Weibull, and the GEV distributions, respectively. The estimates obtained here using the Weibull distribution are comparable to those obtained independently by API (API—American Petroleum Institute, 2007, “Interim Guidance on Hurricane Conditions in the Gulf of Mexico,” API Bulletin No. 2INT-MET). However, the use of objective criteria to identify the optimal distribution suggests that the GEV estimates are to be preferred if the engineer wishes to emphasize the upper tail where extremes are likely to occur. The maximum increase in the SWH100 due to the 2004–2008 season is of the order of 0.9 m to 2.7 m (depending as the distribution). Information generated here is intended to supplement the design recommendations provided by API (American Petroleum Institute, 2007, “Interim Guidance on Hurricane Conditions in the Gulf of Mexico,” API Bulletin No. 2INT-MET).