The San Luis Pass shallow salt dome lies about 7 miles offshore from the Texas coast under about 50 feet of water. A detailed submarine gravity survey was made to determine the outline, thickness and depth of caprock as a guide for test drilling for the evaluation of the dome as a sulphur prospect. There were no drilling contacts on the dome when the work was done. Seventeen test wells were subsequently drilled within the shallow dome outline as estimated from analysis of the gravity results. The caprock found was slightly smaller in area, considerably shallower in depth and of substantially the same thickness as predicted. The caprock material is nearly all gypsum.