BP spokesman Bill Stephens said on Thursday the man was dead but released no details on whether the body was found in the rubble or elsewhere.
Earlier in the day, officials said there were indications the man had checked out and left the refinery after Wednesday's explosion.
About 1800 people work the plant, but it was unclear how many were there at the time of the blast.
The fiery explosion shot flames high into the sky, forced schoolchildren to cower under their desks, and showered plant grounds with ash and chunks of charred metal.
Windows rattled more than 8km from the 480-hectare plant near Houston.
The cause of the explosion was not immediately known.
Most of those who died were contractors for JE Merit Constructors Inc, a field-services provider and subsidiary of Jacobs Engineering Group Inc in Pasadena, California, refinery manager Don Parus said.
About 433,000 barrels of crude oil are processed a day at the plant, producing 3% of the US supply. Other than the unit affected by the blast, the rest of the refinery was running normally, according to Hugh Depland, spokesman for BP, formerly British Petroleum.
Firefighters attack the blaze at
the BP oil refinery in Texas City
He declined to answer questions about the capacity the refinery was running at Thursday or how production would be affected.
Petrol prices could rise slightly because the plant is such a large gas producer. In afternoon trading on Thursday in Europe, the price of unleaded petrol for April delivery was up 2.8 cents.
The explosion happened in a part of the plant used to boost the octane level of petrol. An investigation is under way, BP America president Ross Pillari said on Thursday.
"It's clear that we have a lot of work to do in the coming days to make sure we understand exactly what happened, and we're going to do that," Pillari said. "We are going to put all of our resources into it."
'One big boom'
Federal investigators planned to review the accident.
Wenceslado de la Cerda, a 50-year-old retired firefighter, said the blast shook the ground, rattled windows and knocked ceiling panels to the floor.
"Basically, it was one big boom," he said. "It's a shame that people have to get killed and hurt trying to make a dollar in these plants, but that's part of reality."
Valerie Perez was among those standing vigil outside the refinery fence late on Wednesday, concerned about the fate of her 18-year-old husband, a BP worker.
Wednesday's accident was the
third to hit the town in one year
"I'm nervous," she said, holding back tears.
The plant and town, population 40,000, have dealt with two other refinery accidents within the last year.
The Occupational Safety and Health Administration fined the refinery nearly $110,000 after two employees were burned to death by superheated water in September.
Another explosion forced the evacuation of the plant for several hours last March. Afterward, OSHA fined the refinery $63,000 for 14 safety violations, including problems with its emergency shutdown system and employee training.
Texas City is the site of the worst industrial accident in US history. In 1947, a fire aboard a ship at the Texas City docks triggered a huge explosion that killed 576 people and left fires burning in the city for days.