Vessels used by Royal Dutch Shell PLC to drill for oil off Alaska have safely departed Arctic waters.

Shell announced Sept. 28 it would cease further exploration in the Chukchi and Beaufort seas after spending upward of $7 billion on Arctic offshore exploration.

The company cited disappointing results from an exploratory well drilled in the Chukchi and the unpredictable federal regulatory environment.

Shell experienced transit problems with vessels the last time it drilled off Alaska in 2012.

The Kulluk broke loose from its tow vessel in gale-force winds and ran aground near Kodiak Island. And the Noble Discoverer was fined $12.2 million for violating pollution and safety laws.

Shell spokesman Curtis Smith says both vessels used this year safely reached an Aleutian Islands port. One vessel has departed for Washington state.