Bayer shares soared as much as 11% on Friday on a report that the German company has proposed to pay up to $8 billion to settle more than 18,000 U.S. lawsuits related to its weedkiller Roundup.
The stock was on track for its best single-day gain in a decade as traders said the settlement report from Bloomberg could relieve pressure on Bayer shares.
Bayer, which acquired Roundup and other glyphosate-based weedkillers as part of its $63 billion takeover of Monsanto last year, declined to comment.
Bayer shares have lost more than a third, or roughly 30 billion euros ($34 billion), in market value since August last year, when a California jury in the first such lawsuit found that Monsanto should have warned of the alleged cancer risks from Roundup.
At 1012 GMT, the shares were up 4.8% at 66.02 euros, the top gainer on Germany's blue chip DAX 30 index.
The German drugs and pesticides company has engaged in negotiations with plaintiffs' lawyers, a person familiar with the matter told Reuters.
Bayer said this week that the next U.S. glyphosate lawsuit scheduled to be heard in St. Louis, Missouri, would likely be postponed and the company added on Friday that the following St. Louis case slated for September had been postponed.
Bloomberg said the delays had been pursued by Bayer to allow for undisturbed settlement talks.
The initial unfavourable court rulings in the first three glyphosate cases, heard in California, have at times dragged Bayer's market value below the price tag of target company Monsanto, though share are now trading above that level.
Bayer's Chief Executive Werner Baumann last week said the company would consider settling with U.S. plaintiffs only on reasonable terms, and if it "achieves finality of the overall litigation".
He added at the time the group was "constructively engaging" in a court-ordered process with mediator Ken Feinberg on the cases heard in federal court. Most of the pending cases, however, have been filed with U.S. state courts.
The company, which says regulators and extensive research have found glyphosate to be safe, has previously said it was banking on U.S. appeals courts to reverse or tone down three initial court rulings that have so far awarded tens of millions of dollars to each plaintiff.
Bloomberg cited three sources familiar with the discussions as saying that Bayer's lawyers are seeking an accord to resolve all current and future cases. Talks over cases that have yet to be filed were particularly tricky, the report added.
While Bayer has indicated it could pay $6-$8 billion, plaintiffs' lawyers want more than $10 billion to drop their claims, the report said.
"Progress on settlement is a clear positive to potentially remove what has been the key overhang in shares for a year," Bank of America analysts said in note.
An estimate of a $20 billion hit from the litigation has previously been reflected in the share price, while a likely litigation settlement liability was in the mid single-digit billion dollar range, they added.
But they kept a neutral rating on the stock, citing uncertainty over Bayer's fortunes in the appeals process - with the first appeals verdict expected by the end of the year - and whether a settlement could be achieved before that.
The number of U.S. plaintiffs blaming Roundup and other glyphosate-based weedkillers for their cancer continued to rise by 5,000 to 18,400, Bayer said last week, as a litigation wave showed no sign of letting up.