Two important papers on the geology of Avery Island dome (one of the often mentioned "Five Islands" of S. Louisiana) were published in 1899 and 1931. The present study reports the findings since the discovery of oil in 1942. The history of salt-mine operations is reviewed, present mining practices explained briefly, and the configuration of the salt mass as it is now known is described. Oil sands have been found ranging in depth from 4,500 ft. to 5,600 ft.; 16,456 ft. is the greatest depth to date drilled. The bulk of the proved reserves ranges from about 8,500 to 9,500 ft. in depth and is located on the SW flank. Present drilling is mainly to define new deep reserves on the E flank, or explore for new reserves on the SE flank. Accumulative production totals about 34 million barrels of oil with minor volumes of gas as of May 1, 1958. The total proved reserve is probably about half depleted, with good possibilities for new reserves being discovered on untested or deeper flanks. The structure of the drilled flanks has been found to be a complex of radial faults, salt overhang, and steeply dipping sediments with updip terminations against the shallow piercement-type salt mass. The age of formations penetrated ranges from Recent to the Discorbis zone of the middle Miocene.