The amount of methane hydrates in the northern Gulf of Mexico has been overestimated, according to research by Rice University, Georgia Tech and the Scripps Oceanographic Institute. The marine sediments are likely too warm and salty to hold the large quantities of methane hydrates originally thought to exist beneath the ocean floor. Researchers reported that high-resolution geophysical and geochemical data for two representative sites off the coast of New Orleans suggested that previous estimates for the region should be revised sharply downward. The abundance of salt is the culprit. The thermal properties of salt and the presence of salt in the pore spaces retards the formation of methane hydrates. The study, funded by the National Science Foundation, is continuing. The researchers are working toward a quantitative estimate of the gas hydrates at the sites, but the deposits appear to be thin to nonexistent. Methane gas hydrates are formed when methane combines with water at low temperatures and high pressures and forms an ice-like solid. The deposits are found throughout the world, mainly in sediments tens to hundreds of meters below the sea floor in water depths greater than 500 meters. They can occur as chunks and as concentrated layers. The scientists used high-resolution seismic equipment to image the sites; analyzed water samples from sediment cores and developed chemical profiles; measured heat flows; and collected data on fluid flux from the sea floor. Methane hydrates are being investigated as a potential energy source. Oil and conventional gas explorers are also interested in safety issues they may pose during deepwater drilling, such as destabilization of the sea floor.