Shell Nigeria Exploration and Production Co., this week confirmed that Nigerian oil remediation authorities recommended "an administrative fine" said to total $5 billion for an incident at the Bonga field.
The company, in a statement, said it would contest the proposed penalty.
"Shell Nigeria Exploration and Production Co. will challenge any attempt to impose such a penalty," Managing Director Chike Onyejekwe said.
The Nigerian subsidiary said there was no legal basis for the fine, saying it responded "professionally and diligently" to the Bonga spill.
Shell in December closed operations at the offshore Bonga production platform following a leak from an export line feeding a tanker. The company said preliminary estimates indicated 40,000 barrels of oil spilled, making it one of the worst in Nigeria in decades.
Onyejekwe said there were some parties in Nigeria that claimed the oil spill impacted the shoreline and regional waterways. Hearings in Abuja, he added, suggested otherwise.
"We deeply regret that this incident took place but as a responsible operator and corporate citizen we responded to it professionally and effectively and that everything we did was in cooperation with the authorities and in compliance with the regulations," he said in a statement.
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