An eleven strong American team from Western Kentucky University – Hoffman Environmental Research Institute visited Mulu towards the end of 2009. Led by Pat Kambesis, the project conducted over a 10-day period, was under the direction of National Park manager Brian Clark. One of the main objectives of the trip was to document the size and length of Deer Cave accurately, as it contains one of the largest cave passages in the world. A combination of total-station type survey methods and standard cave survey techniques were used to measure width, height, and volume of cave passages and to georeference in-cave features accurately.
The 2009 survey effort increased the known passage length to 4.1 kilometers (2.5 miles) and connected Langs Cave, another show cave within the park, to the Deer Cave System. Maximum passage width of Deer Cave System documented in this effort was 168.7 meters (553 feet) and ceiling heights averaged well over 120 meters (394 feet). The main entrance of Deer Cave was measured at 146 meters (478 feet) and the Garden of Eden Entrance was measured to be 140 meters (450 feet) in width.
The survey revealed the height of the undescended Deer Cave Aven skylight at 305 meters, which places it among the three deepest in southeast Asia. The highest elevation roof passage (and probably the oldest) in the system was the Antler Passage measured at 226 meters (741 feet) above the main cave floor.
Further analysis of the data and a new detailed map will be produced, as well as a 3-D model of the cave system.