The safety of massive oil tanks in Alaska is being questioned this week as the House of Representatives prepares to debate opening more of the state's environmentally protected areas to oil exploration.

The tanks, owned by Alyeska Pipeline Service - a company owned by oil giants BP, Exxon and ConocoPhillips - were investigated several years ago and deemed fit for service. But this month a member of the Joint Pipeline Office (JPO), which combines federal and state regulators to ensure the safety of Alaska's oil industry, approached Glen Plumlee, a former senior financial analyst at Alyeska, to discuss the situation again, Mr Plumlee said.