Under master James C. Spillane, Puerto Rican arrived in San Francisco Bay on October 25, 1984, and called at Richmond and Alameda. She loaded a cargo of 91,984 barrels of lubrication oil and additives, took on 8,500 barrels of bunker fuel, and departed for sea shortly after midnight on October 31, bound for New Orleans. At 3:24 a.m., as she was disembarking the pilot outside the San Francisco Bay Entrance Channel, an explosion occurred near the No. 6 center-independent tank, which blew flames several hundred feet into the air, knocked the pilot and two crew members into the water, and folded back an immense section of the deck measuring nearly 100 feet square. The pilot boat San Francisco rescued pilot James S. Nolan and third mate Philip R. Lempiere, but able seaman John Peng was lost.

Response by the Coast Guard was immediate, and the burning tanker was towed to sea in order to minimize the chance of a disastrous oil spill on the sensitive areas of San Francisco Bay, the adjacent ocean shoreline, and the Gulf of the Farallones National Marine Sanctuary. By the following afternoon, the fires had been extinguished, but on November 3, Puerto Rican, her hull weakened by explosion and fires, broke in two sections, releasing 30,000 barrels of oil into the water. The stern section, containing 8,500 barrels of fuel oil, sank at 37 degrees, 30.6 minutes north latitude and 123 degrees, 007. minutes west longitude, one mile inside the boundaries of the sanctuary. The remains at a depth of 1,476 feet have been thoroughly surveyed by side-scan sonar. Oil still leaks slowly from the vessel. Delgado & Haller