Shell Oil's Polar Pioneer rig left Alaska's Dutch Harbor for Port Angeles, Washington, on Wednesday.
The energy giant's other Arctic rig, the Noble Discoverer, left Dutch Harbor for Everett, Washington, on Monday.
Other ships in Shell's Arctic fleet are expected to leave Alaska over the next couple of weeks, and the company has not disclosed the fate of the 400 employees who have worked on the project in Anchorage.
But the departure of the 30-story-tall Polar Pioneer is the most visible sign that Shell's 8-year hunt for oil in the Arctic Ocean has come to an end.