US President Barack Obama's administration is expected to push through long-delayed safety measures for the nation's sprawling network of oil pipelines in its final days.
The move is despite resistance from industry and concern that incoming president Donald Trump may scrap them.
The measures are aimed at preventing increasingly frequent accidents such as a 176,000-gallon spill that fouled a North Dakota creek earlier this month. Thousands more spills over the past decade caused 2.5 billion US dollars in damages nationwide and dumped almost 38 million gallons of fuel.
Fights over pipelines have intensified in recent years, illustrated by the dispute over TransCanada's Keystone XL plan and efforts by American Indians to stop the Dakota Access Pipeline from crossing beneath the Missouri River near the Standing Rock Sioux Reservation.
The US Department of Transportation proposal covers roughly 200,000 miles of lines that cross the country and carry crude, gasoline and other hazardous liquids.
Environmental and safety advocates have criticised the agency's commitment to tightening oversight of that network after a key safety feature - automatic valves that quickly shut down ruptured lines - was omitted from a draft rule published in 2015.
Further revisions sought by the petroleum industry could make the rule largely ineffective, said Carl Weimer with the Pipeline Safety Trust. But keeping the proposal intact would expose it to a legal challenge or reversal by a Republican-controlled Congress and Mr Trump, an enthusiastic advocate for fossil fuels whose administration would enforce the new safety provisions, Mr Weimer added.
"We already viewed it as an incremental step. If they water it down at all or extend the timelines, it's going to be an even smaller step," he said.
Regulators began crafting the new rule after a 2010 Michigan pipeline break released almost 1 million gallons of crude into the Kalamazoo River. It has languished amid industry criticisms, interventions from Congress and the bureaucratic inertia of the federal regulatory process.
A recent boom in domestic drilling saw accident rates for pipelines increase by roughly a third. The number of hazardous liquid pipeline accidents in the US increased from 350 in 2010 to 462 in 2015.
The Transportation Department proposal calls for tougher inspection and repair criteria, leak detection systems on more lines and other measures to cut risk. Companies would also be required to inspect lines after flooding or other extreme events, a provision adopted after a 2011 ExxonMobil pipeline break spilled 63,000 gallons of crude into Montana's Yellowstone River.
It is currently under review by the White House Office of Management and Budget. Final adoption is anticipated in late December, said Allie Aguilera, government affairs director of the Transportation Department's Pipeline and Hazardous Materials Safety Administration.
Industry representatives argue it would cost companies 600 million dollars a year and almost 5 billion dollars over the next decade. That is almost 30 times the government's estimate of 22.5 million dollars annually.
Association of Oil Pipe Lines vice president John Stoody said the rule would force pipeline owners to immediately repair lines with microscopic cracks or traces of corrosion. Currently, the industry is allowed to monitor smaller defects and schedule repairs later.
"It has the potential to distract us away from higher-priority safety issues," Mr Stoody said of the more stringent repair criteria.
Advocates say the rule is particularly important for rural areas. Current regulations apply primarily to lines in "high consequence areas" with large populations or environmentally sensitive features such as drinking water supplies.
Lines outside those areas are not required to be inspected with mechanical devices known as "pipeline pigs", which travel inside lines looking for flaws.
"This is the first time (the Department of Transportation) is saying you have to inspect them" using the devices, Mr Weimer said.
The Bellingham, Washington-based safety trust was formed after three children were killed when a gasoline pipeline broke in 1999, leaking fuel for one-and-a-half hours before it exploded.
The 176,000-gallon Belle Fourche Pipeline spill near Belfield, North Dakota occurred on December 5 on a line outside a high consequence area. True Companies of Casper, Wyoming, which owns the line, said it uses pipeline pigs for inspections, a claim confirmed by federal officials. Company spokeswoman Wendy Owen could not specify when that last occurred.
The six-inch line can carry up to 1 million gallons of crude daily. It is unclear how long it was leaking before the spill was discovered. By then, oil had travelled four-and-a-half miles down a tributary of the Little Missouri River, according to the Environmental Protection Agency. About 76,000 gallons of oil has been recovered, Ms Owen said.
Electronic monitoring equipment on the line failed to detect any problems, the company said.
The American Petroleum Institute acknowledged it was seeking revisions to the administration's safety proposal but declined to specify the changes it wants.
In a 65-page cost-benefit analysis, the petroleum institute criticised federal officials for underestimating the costs and amount of work needed for companies to comply. The group described the rule as a "significant expansion of regulatory oversight".
Minimal federal oversight of pipelines in rural areas has left officials in some states overwhelmed with the task of policing the industry.
Pressured by landowners, farmers and environmentalists, North Dakota will put a state rule into effect on January 1 to increase inspections of smaller pipelines known as gathering lines. The federal proposal requires only that companies document spills from the lines.
Kevin Pranis, a spokesman for the Labourers District Council of Minnesota and North Dakota, which represents some workers building the four-state, 3.8 billion dollar Dakota Access Pipeline, said his group welcomes "sensible" regulation for the industry.
"The pipeline industry is under scrutiny like never before," Mr Pranis said.