In the Senate, the top members of the Energy Committee urged federal pipeline regulators to probe the corrosion. They hinted that more hearings or legislative actions were in store if they do not get satisfactory answers.

Congress has recessed until September. But lawmakers concerned about US gasoline pump prices above US$3 a gallon were voicing concerns about Prudhoe Bay, where pipeline corrosion threatens to shutter about 8 percent of US crude oil production.

House Energy Committee Chairman Joe Barton, said his hearing will focus on BP's "management of its corrosion control in its oil-transit lines."

Barton, a Texas Republican, did not name witnesses yet, but BP officials are nearly sure to be called to appear.

Senate Energy Committee Chairman Pete Domenici, a Republican, and ranking Democrat Jeff Bingaman asked Thomas Barrett, the US government's top pipeline regulator, for data on why the BP on Sunday began shutting down the field.

"It seems to us that this failure should not have happened," said the senators, both from New Mexico.

"We will continue to monitor this situation, and, if necessary, we will take appropriate action," the senators said in a letter to Barrett, the head of the Transportation Department's Pipeline and Hazardous Materials Safety Administration .

The lawmakers said the department should fully investigate the reasons why BP failed to use internal inspection devices known as smart pigs to find the pipeline corrosion.

"Early reports of the discovery of 16 anomalies at 12 locations in a three-mile area of the Eastern Area (of the field) are distressing, and, if true, inexcusable," the senators said.

BROKEN PIPELINES

The problems with the eastern oil transit line come only a few months after another corroded transit line on the western side of the field ruptured and spilled at least 200,000 gallons of crude oil, prompting a federal regulatory crackdown and a criminal investigation.

A decision on whether to keep operating the western half of the field had been expected by Friday, but BP said on Thursday it was delaying this deadline until early next week.

In an interview, Barrett said he had not seen any data that would compel the government to order BP to shut down the western half of the field. But he wants to see more data.

The agency will likely require BP to provide data from a scan of the bottom third of the pipeline before allowing the company to continue operating the pipelines.

BP confirmed earlier on Thursday that it was only scanning the bottom sixth of the pipelines.