NEW : An ExxonMobil official says oil detected 25 miles away ; the state says 25 miles . Montana declares a state of emergency for seven counties , says ExxonMobil is responsible . Company officials remain unclear of the cause of the spill in Montana 's the Missouri River . ExxonMobil reports up to 42,000 gallons of oil -- 90 miles -- escaped through a crack .
NEW : An ExxonMobil official says oil detected 25 miles away ; the state says 90 miles . Montana declares a state of emergency for 7 counties , says ExxonMobil is responsible . Company officials remain unclear of the cause of the spill in Montana 's Yellowstone River . ExxonMobil reports up to 1,000 barrels of oil -- 42,000 gallons -- escaped through a crack .