The most recent comprehensive report on the geology and development of the Jefferson Island dome, Iberia and Vermilion parishes, Louisiana, was published in 1935. The present publication adds the findings from flank drilling, all of which has occurred in the last 15 years. Oil and gas sands have been found ranging in depth, with one exception, from 7,500 feet to 8,700 feet, with cumulative production totaling about 2½ million barrels to January, 1952. The structure of the flank has been found to be a complex of radial faults and steeply dipping sediments with updip termination against the salt mass. The age of formations penetrated ranges from Recent through upper and possibly into marine (middle) Miocene. Development and exploration continue at a moderate rate. The alt is found to have overhang between the depths of 1,000 feet and 3,000 feet with a broad shoulder present at a depth of about 10,000 feet.