Citi analyst Robert S. Morris said in a research note that any appeal process could extend for up to 10 years. He lowered his rating on shares of The Woodlands, Texas-based oil and natural gas exploration and production company to "neutral" from "buy" and dropped his target price to $86 from $108.
"This would create a substantial overhang on Anadarko's stock price, in our opinion," the analyst wrote.
Investors dislike the uncertainty of unresolved litigation hanging over a company's stock.
Morris added that it is difficult to gauge the possibility or magnitude of any settlement, but he thinks Anadarko has the ability to make a worst-case payout of $14.2 billion before taxes without putting day-to-day operations in jeopardy.
Tronox also has accused its former parent of sticking it with hundreds of millions of dollars of environmental legacy lawsuits, including the costs of cleaning up contaminated soil near plants that closed decades ago under different owners.
Tronox said Thursday that 88 percent of any judgment it eventually receives will go to trusts and other government entitles to help remediate polluted sites. The remainder will go to another trust to compensate those injured "as a result of Kerr-McGee's environmental failures."
Anadarko shares sank 7.8 percent, or $6,50, to $77.17 in midday trading Friday. The stock had climbed nearly 13 percent so far this year through Thursday.
Meanwhile, shares of Stamford, Connecticut-based Tronox jumped 6.7 percent, or $1.41, to $22.58 in midday trading.