An underwater LNG release test was conducted to understand the phenomena that occur when LNG is released underwater and to determine the characteristic of the vapor emanating from the water surface. Another objective of the test was to determine if an LNG liquid pool formed on the water surface, spread and evaporated in a manner similar to that from an on-the-surface release of LNG. A pit of dimensions 10.06 m x 6.4 m and 1.22 m depth filled with water to 1.14 in depth was used. A vertically upward shooting LNG jet was released from a pipe of 2.54 cm diameter at a depth of 0.71 m below the water surface. LNG was released over 5.5-min duration, with a flow rate of 0.675 +/- 0.223 L/s. The wind speed varied between 2 m/s and 4 m/s during the test. Data were collected as a function of time at a number of locations. These data included LNG flow rate, meteorological conditions, temperatures at a number of locations within the water column, and vapor temperatures and concentrations in air at different downwind locations and heights. Concentration measurements were made with instruments on poles located at 3.05 m, 6.1 m and 9.14 m from the downwind edge of the pit and at heights 0.46 m, 1.22 m, and 2.13 m. The phenomena occurring underwater were recorded with an underwater video camera. Water surface and in-air phenomena including the dispersion of the vapor emanating from the water surface were captured on three land-based video cameras. The lowest temperature recorded for the vapor emanating from the water surface was -1 degrees C indicating that the vapor emitted into air was buoyant. In general the maximum concentration observed at each instrument pole was progressively at higher and higher elevations as one traveled downwind, indicating that the vapor cloud was rising. These findings from the instrument recorded data were supported by the visual record showing the "white" cloud rising, more or less vertically, in air. No LNG pool was observed on the surface of water. Discussions are provided on the test findings and comparison with predictions from a previously published theoretical model. (c) 2011 Elsevier Ltd. All rights reserved.