BP Alaska, which operates the pipeline, has denied claims it failed to maintain it properly.
The spill was detected on 2 March and plugged. Local environmentalists have described it as "a catastrophe".
BP is already facing a probe into a blast at a Texas refinery in March 2005 in which 15 people died and 170 were injured.
The firm has settled several cases resulting from the explosion and put $1.2bn (£641m) aside to resolve legal disputes.
BP recently announced a complete review of its global operations following last year's Texas blast.
File on 4's Julian O'Halloran looks at these two incidents and investigates charges that BP courted disaster by cutting corners on safety and maintenance.
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