LAUREL, Montana -- The initial cleanup along the oil-fouled Yellowstone River could be tested Tuesday as rising waters make it harder for Exxon Mobil ( XOM) to get to areas damaged by the crude spilled from a company pipeline. The National Weather Service predicts the Yellowstone River, swelling with mountain snowmelt amid hot summer temperatures, will peak at Billings on Tuesday afternoon -- a day after Exxon Mobil Pipeline Co. President Gary Pruessing promised to do "whatever is necessary" to mop up oil spilled from the duct at the river bottom. That pledge included sending crews to walk the river banks in search of pooled oil once the flooding river recedes. The 12-inch pipeline burst Friday upstream from a refinery in Billings, where it delivered 40,000 barrels of oil a day. Up to 1,000 barrels, or 42,000 gallons, of crude oil oozed into the legendary Yellowstone before the leak was stopped, according to Exxon Mobil estimates. After downplaying assertions from state and federal officials that damage from the spill was spread over dozens of miles, Exxon Mobil acknowledged under political pressure Monday that the scope of the leak could extend far beyond a 10-mile stretch of the river. Company officials also said their statements were misconstrued. "We're not limiting the scope of our cleanup to the immediate site," Pruessing said at a news conference along the river near Laurel, as crews mopped up oil in the background. "We are not trying to suggest in any way that that's the limit of exposure." The 20-year-old Silvertip pipeline followed a route that passes beneath the river. It was temporarily shut down in May after Laurel officials raised concerns that it could be at risk as the Yellowstone started to rise. Also twice in the last year, regulators warned Exxon Mobil of several safety violations along the line. The company decided to restart the line after examining its safety record and deciding it was safe, Pruessing said. The cause of the rupture has not yet been determined, but company and government officials have speculated that high waters in recent weeks may have scoured the river bottom and exposed the pipeline to damaging debris.