BILLINGS, Mont. (AP) — U.S. officials have rejected Exxon Mobil Corp.'s request to reconsider a $1 million penalty imposed against the oil giant over a 63,000-gallon crude spill into Montana's Yellowstone River. The U.S. Department of Transportation on Friday ordered the Texas company to pay the penalty within 20 days. Safety regulators said Exxon Mobil failed to adequately heed warnings that its 20-year-old Silvertip Pipeline was at risk from flooding.