Elsewhere, other groups are eyeing these aging platforms. An architectural organization based in London hosted a competition several years ago calling for design plans to build a prison on new or refurbished platforms. “Sea-steaders” have proposed buying platforms to create offshore communities. Their hope is to escape urban noise, crowds, crime and pollution, or potentially to move beyond the reach of certain laws and taxes in international waters.

In the United States, a federal rigs-to-reefs program has overseen the sinking of hundreds of platforms in American waters. Thousands more are coming up for decommissioning in the Gulf of Mexico over the next several years.

The federal program allows some oil and gas companies to convert their decommissioned rigs to reefs instead of requiring the companies to remove them. If the rigs-to-reefs option is expected to be less expensive than removal, the platform owner pays half the estimated savings to the state agency receiving the former platform. In Louisiana, the program is very popular among anglers because the artificial reefs attract fish. It has been opposed, however, by the Louisiana Shrimp Association, because the sunken rigs prevent shrimp boats from trawling the seafloor.

SUPPORTERS of the program say that aside from environmental benefits, sinking rigs helps keep energy prices lower for consumers by making drilling more affordable. “That’s exactly the problem,” said John Hocevar, oceans campaign director for Greenpeace. By saving drilling companies money, he said, rigs-to-reefs programs only promote more drilling, hide the true costs of this type of energy extraction and deepen overall dependence on fossil fuels. The repurposing of platforms built to be temporary also imposes long-term maintenance and liability burdens on the public, he added, enabling the companies that originally profited from them to avoid responsibility for their ultimate fate.

Dr. Sharul Sham bin Dol, the director of the petroleum engineering department at Curtin University in Sarawak, Malaysia, said that the platforms could work extremely well for fish hatcheries. “As fish cages hang down into the water below, they also reduce transportation and operational costs,” he said.