What happened

A helicopter pilot observed bubbles at the surface of Cook Inlet above Hilcorp's eight-inch Middle Ground Shoal fuel-gas pipeline, about six miles offshore from Nikiski. Hilcorp reported the leak to regulators, reduced the line's pressure and then closed block valves to isolate it, shutting two offshore oil-production platforms as a precaution. The released product was processed dry natural gas containing about 98.67 percent methane; regulators said the volume released into the water and the cause were unknown. The same subsea line had leaked in 2017. The Pipeline and Hazardous Materials Safety Administration ordered Hilcorp to make temporary and permanent repairs and submit a plan to replace the approximately 55-year-old pipeline, citing its leak history.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.