Robert Collins, an assistant attorney general in Montana's natural resource damage program, said the state is trying to determine whether there are grounds for a claim against Exxon Mobil.
Around 1,200 barrels of oil spilled from Exxon Mobil's Silvertip pipeline into the Yellowstone River near Billings in early July. Flooding slowed cleanup efforts and teams were sent in to remove debris soaked with oil after water levels dropped. U.S. officials said less than 1 percent of the total amount spilled was recovered.
"All of the environmental issues are not yet resolved," Collins was quoted by the Billings (Mont.) Gazette as saying.
Collins added that state officials sent Exxon invoices totaling around $230,000 for the cost of investigating the incident. Exxon announced Jan. 19 it agreed to a $1.6 million settlement for damage to the river and nearby environment.
A spokeswoman for the oil company said Exxon had no information about the state's latest action and couldn't comment on legal matters.