The South Pass Block 27 field, located in the coastal waters of Louisiana, is associated with an intermediate-depth salt dome. Only the N. flank of this salt-dome structure has been explored and developed, but proved reserves already exceed 200 million barrels of oil and 220 billion cu. ft. of gas. The field ranks high among the giant oil fields of Louisiana in terms of ultimate oil recovery. The unexplored areas show excellent productive promise, and the South Pass Block 27 field may eventually yield the largest field reserve yet found in the offshore waters of the Gulf of Mexico. All production is from sands of Plio-Miocene age between the depths of 6,000 and 10,400 ft. One hundred and fifty-three producing wells have been completed, and cumulative production from these wells was 12,251,700 barrels of oil and condensate and 10,016,341 MCF of gas through Sept. 1959. Active development of the field is still in progress. Contemporaneous faults traversing the structure have a marked effect on structural configuration. These faults are classified as contemporaneous because movement along the fault plane appears to have been contemporaneous with deposition over a part of the fault history. This type of faulting, commonly encountered in the Gulf Coast, is characterized by a greater thickness of sediments in the downthrown block than in the upthrown block and by an increase in throw of the fault with increasing depth. The major part of proved oil reserves is entrapped in the western part of the N. flank on the upthrown side of a large contemporaneous fault which strikes essentially N.-S. Maps contoured on top of the "D4" sand, the "N4" sand, and salt are included to illustrate the structural aspects of the field. These maps are supplemented by structural cross sections and schematic diagrams. In addition structure maps on 4 typical producing beds are presented to delineate the more important producing areas of the field.