Six Greenpeace activists have boarded a Russian offshore oil rig in protest over gas and oil exploration in the Arctic, the group says.

BBC: Greenpeace activists board Russian Gazprom oil platform

When an offshore oil rig is outdated, or can no longer cost-effectively pump oil, most countries require that the oil rigs be wholly decommissioned.

FORBES: Environmental Scientists Urge That Decommissioned Oil Rigs Be Transformed Into Artificial Reefs

Chevron sunk an offshore oil rig in 1937 in 14 feet of water and by 1947 drillers were working on rigs out of sight of land.

FORBES: On The Gulf Coast, Somebody Will Pay

As a precaution, many oil companies were evacuating rig workers and support personnel from offshore installations in the area.

MSN: Tropical Storm Debby forms in Gulf; Louisiana warned

The explosion in April of that year of a drilling rig in the Gulf of Mexico triggered the largest offshore oil spill in the country's history.

WSJ: Should the U.S. Expand

The London-based company has lost more than a third of its stock-market value since April 20, when one of its gulf wells blew out, destroying the Deepwater Horizon drilling rig, killing 11 men and triggering the worst offshore oil spill in U.S. history.

WSJ: BP Shakes Up Management

In California, an offshore drilling rig stained the coast of Santa Barbara with more than 3 million gallons of crude oil.

CNN: Challenges ahead for a changing Earth

John McCain touts offshore drilling as a solution to producing more oil, and recently held a press conference on an oil rig in the Gulf of Mexico to make his point.

CNN: Stripper wells try to get more oil from ground