"Our first and foremost concern will be finding the 18 people that are missing," Coast Guard spokeswoman Krys Hannum said.
Hannum said there was no reason to believe the explosion was anything other than an accident.
Two Coast Guard patrol boats and a C-130 airplane and helicopter were conducting the search about 50 miles off Virginia's Eastern Shore.
"We're going to search as long as it's reasonable and hope they're alive," she said.
But with water temperatures below 50 degrees, the likelihood of additional survivors being found grew increasingly slim. Hannum said some of the crew members were sleeping at the time of the explosion and some were on deck, so it's unlikely that they were wearing gear that would protect them from the cold water.
The survivors were rescued from a life raft within three hours of the accident and flown to Sentara Norfolk General Hospital. They were treated for conditions including hypothermia and had to be decontaminated after being found covered with a petroleum-based substance.
One survivor was in serious condition, two were in fair condition and the three others were released Sunday morning, hospital spokeswoman Vicky Gray said. Two Coast Guard personnel treated for minor injuries also were released.
"They look like they've been through an ordeal and they're very introspective about what happened," Gray said of the rescued crewmen, who are Filipino and did not speak English. "They're very quiet, subdued, like you would expect."
The crew members have declined interview requests, Gray said. Hospital chaplains helped the crew talk to their families in the Philippines by telephone.
Coast Guard officials said that most of the ethanol spewed from the tanker had evaporated, but fuel from the ship's storage tanks has formed a 9-square-mile oil slick in the Atlantic.
Guardsmen don't yet know how much of the fuel aboard the ship spilled; but they say it was carrying 48,000 gallons of stored diesel fuel and 193,000 gallons of fuel oil.
Environmental officials are most concerned about the fuel oil, a sticky, heavy, molasses-like substance that was used to power the vessel.
"That's what we're really keeping an eye on. We don't want that stuff to reach the shoreline," said Mike Sharon, chief of the emergency response division of the Maryland Department of the Environment.
Computer models drawn by scientists at the Coast Guard and the National Oceanic and Atmospheric Administration predict the spill will wash out to sea and not glom onto the shores of Maryland or Virginia, said Chief Warrant Officer Gene Maestas of the Coast Guard.
The 570-foot Bow Mariner was en route from New York to Houston Saturday when it sank in 200 feet of water. Lt. Chris Shaffer of Ocean City (Md.) Emergency Services said the explosion came after a fire started on the deck of the ship.
The ship is a chemical tanker built in 1982 and is managed by a Greek company, Ceres Hellenic Shipping Enterprises Ltd. A company spokesman said the ship had a crew of 24 Filipinos and three Greeks.
A spokesman for Norway-based Odfjell, the commercial operator and owner of the Singapore-flagged ship, declined to speculate on what caused the accident.
"We are very grieved about having to report that Bow Mariner has gone down and that many seamen have lost their lives," company chairman Dan Odfjell said.
Tony Redding, spokesman for Ceres Hellenic, said the company was sending a technical crew from Greece on Sunday to assist the Coast Guard. Odfjell hired Marine Spill Response Corporation, which dispatched a cleanup ship to standby, Sharon said.
The Bow Mariner underwent two routine inspections in 2003, Ceres Hellenic said in a statement. No problems were found in January, and five minor deficiencies were found in October, including a defective crew shower and the need to update a log book. The issues were corrected and the ship sailed without delay, the company said.
Scientists with the Coast Guard's Marine Safety Office were preparing the environmental cleanup, Maestas said. A likely method would be using inflatable booms to surround the spill and shift it toward pumps that would skim the oil and funnel it into a nearby barge, he said.
Ethanol, an alcohol-based fuel additive made from corn and other starch crops, is considered environmentally clean. It is water-soluble and isn't floating atop the waters of the Atlantic, Sharon said.
"Because it mixes with the water, it's got the whole ocean to dilute it out," he said. "You don't see the kind of containment issues you have with oil."
By Sonja Barisic