He said the transit lines weren't considered high risks for corrosion-related leaks because they carry only oil that's had corrosive water removed, leaving the oil ready for shipment to market. The water is removed in processing plants that are scattered across the oil field and are linked by the transit lines.

BP uses ultrasonic testing to find weak spots in the pipelines. BP managers thought this testing was good enough to find leaks, but Hedges conceded Monday that those tests, performed at random points along the pipelines, were inadequate.

"My suggestion now is we just didn't do it in the right spots," he said.