DENVER — For several days last month, Steven Jensen smelled the oil, wafting up over his rolling wheat farm near Tioga.

But in that part of northwestern North Dakota, where the rush to tap the Bakken shale field is roaring, the scent of crude is hardly uncommon. It was not until Sept. 29 that Mr. Jensen came across a six-inch spurt of oil gurgling up from his land and reported a spill.

As it turned out, a Tesoro Logistics pipeline had ruptured, spreading more than 865,000 gallons of oil across seven acres of Mr. Jensen’s farm. The spill is one of the largest inland oil pipeline accidents in the United States.

State officials, who responded to the spill after being notified by Tesoro, said the oil posed no immediate environmental risk. Fortunately, they said, the accident occurred in a remote area, away from water and homes. But the rupture has raised fresh concerns about the ability of pipeline companies to detect problems before it is too late.