But Pemex acknowledged in a report that starting in late 2011, a series of smaller blasts and fires, mainly at refineries and petrochemical plants, had "seriously impacted" its safety rate. It said the rate of injuries per million hours had risen to 0.54.
Mexico City-based oil analyst David Shields said he was pessimistic that any one particular accident would have a real impact on the broader push for reform.
"What they really do is spark a certain amount of indignation, most of the time they don't result in changes," he said. "At the end of the day, things don't seem to work out."
Before the pipeline blast in Reynosa, Pemex's last big accident was in 2007, when a sudden storm hit an offshore oil rig, killing 22 workers.
Thursday's explosion occurred at about 3:45 p.m., just as the administrative shift was about to end. It hit the basement and three floors, where as many as 250 people work, Lozoya said. The floors collapsed in the 14-story administrative building at the headquarters office complex, which was built starting in the late 1970s. Some 10,000 people work there daily. Lozoya said about 1,700 work in the building affected.
To the untrained observer, the offices appeared to be showing signs of age surprising for the headquarters of a major oil company. The elevators were often out of service or crept slowly between floors. Its bathrooms were dirty and the floors were worn.
Gabriela Espinoza, 50, a Pemex secretary for 29 years, was on the second floor of the tower when she said she heard two loud explosions and a third smaller one.
"There was a very loud roar. It was very ugly," she said.
Espinoza's co-worker, Tomas Rivera, 32, worked on the ground floor in the building where the explosion occurred and said the force knocked him to the basement, fracturing his wrist and jaw. The injured were taken to two Pemex hospitals and other facilities, including the Red Cross hospital in the Polanco neighborhood near the oil company's headquarters. Relatives huddled in the waiting room for news of their loved ones. Some walked out of meetings with the hospital social worker joyous, while others came out crying.
Lozoya said Pemex operations continue uninterrupted despite the blast and that the company is producing 2.57 million barrels of oil per day.
Pemex, created as a state-owned company in 1938, has nearly 150,000 employees, according to its website, with $111 billion in sales. Pena Nieto, who took office in December, has made Pemex reform the center of his platform, with a plan to pump new investment into a company whose profits feed much of Mexico's federal budget, but which has fallen behind other oil companies in production, technology and exploration.
Shortly before the explosion, Operations Director Carlos Murrieta reported via Twitter that the company had reduced its accident rate in recent years. Most Pemex accidents have occurred at pipeline and refinery installations.
AP writers Katherine Corcoran, Olga R. Rodriguez and Adriana Gomez contributed to this report.
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