ANCHORAGE, Alaska -- The stars lined up -- almost -- for Shell Oil to drill exploratory wells this year in off Alaska's north coast.

The Arctic Ocean was on record pace for low sea ice. The Obama administration gave a qualified green light to drilling. Two drill ships and a flotilla of support vessels were staged off prospects.

But as the open water season wound down, Shell announced last week it would limit drilling to time-consuming preparation for an offshore well. The final straw for the decision: damage during testing Sept. 15 to an undersea containment dome, a key to the company's spill response system.

Environmentalists cheered the setback. Shell Oil President Marvin Odum says he considers it a temporary impediment in the long-term quest to open a petroleum frontier.