COEUR d'ALENE - Probing for a possible fuel leak, ConocoPhillips investigators today are scheduled to get results back from acoustic testing completed on a 6-mile stretch of pipeline through North Idaho.

The company is investigating the stretch of the Yellowstone Pipeline between Enaville and Cataldo after a slow drop in pressure was detected a week ago today.

On Friday, what the company called a "smart ball" was floated from Enaville to Cataldo in fuel inside the 10-inch diameter pipeline, ConocoPhillips spokesman Jeff Callender said.

The ball-shaped acoustic device records sound as it travels through the pipeline, tracking its progress foot-by-foot, allowing the company to pinpoint possible irregularities in the line.

"We have pretty good confidence that it will identify the area that we need to look at," said Callender.

The device was scheduled to be pulled out at Cataldo late Friday, and an analysis of the data from it would then be undertaken.

The pipeline runs along the North Fork of the Coeur d'Alene River, and crosses under the river in a couple places.

Callender said the company hasn't detected a leak, and it still isn't certain what caused the pressure loss. No fuel is unaccounted for, he said.

A pressure drop in the pipeline could be caused by a variety of factors and forces, including rapid temperature changes and acts of vandalism.

The pipeline carries fuel from Missoula to Spokane.

The pipeline transports both gasoline and diesel, and had unleaded gasoline in the line when the loss of pressure was detected.

The company conducted aerial surveillance and had workers walking the pipeline to identify any problem. Those efforts have stopped, while investigators focus on the acoustic test, Callender said.

The company has installed containment booms along several stretches of the river as a protective measure.

ConocoPhillips is the majority owner and operator of the Yellowstone Pipeline, which was installed in 1954, he said.