Beaked whales are deep diving elusive animals, difficult to census with conventional visual surveys. Methods are presented for the density estimation of beaked whales, using passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period during and following the Deepwater Horizon oil spill (2010\u20132013). Beaked whale species detected include: Gervais\u2019 (Mesoplodon europaeus), Cuvier\u2019s (Ziphius cavirostris), Blainville\u2019s (Mesoplodon densirostris) and an unknown species of Mesoplodon sp. (designated as Beaked Whale Gulf \u2014 BWG). For Gervais\u2019 and Cuvier\u2019s beaked whales, we estimated weekly animal density using two methods, one based on the number of echolocation clicks, and another based on the detection of animal groups during 5\u2009min time-bins. Density estimates derived from these two methods were in good general agreement. At two sites in the western GOM, Gervais\u2019 beaked whales were present throughout the monitoring period, but Cuvier\u2019s beaked whales were present only seasonally, with periods of low density during the summer and higher density in the winter. At an eastern GOM site, both Gervais\u2019 and Cuvier\u2019s beaked whales had a high density throughout the monitoring period.<\/p>\n