New turn in $19-billion litigation.

By Roger Parloff, senior editor

FORTUNE -- In filings Friday morning in federal court in Manhattan, Chevron has submitted statements from the top two scientific experts for the Ecuadorian plaintiffs suing the company for alleged oil contamination, disavowing essentially all of their previous findings and conclusions in the case -- findings that formed the purported basis for a $19 billion judgment handed down by an Ecuadorian provincial court against Chevron in February 2011.

"I disavow any and all findings and conclusions in all of my reports and testimony on the Ecuador Project," writes Douglas Beltman, the executive vice president of Boulder-based Stratus Consulting, who headed the firm's assignment. "I deeply regret that I allowed myself and my company to be used in the Lago Agrio Litigation in the way that we were."

"I am not aware," he writes later in the report, "of any scientific data that shows that any adverse health effects are caused by contamination from petroleum operations in the Oriente" -- i.e., the Eastern provinces of Ecuador where Texaco performed drilling operations between 1964 and 1992. (Texaco was acquired by Chevron (CVX) in 2001.)

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In 28-page and 16-page declarations, Beltman and the No. 2 environmental expert on the project, Ann Maest, state that the plaintiffs' chief U.S. lawyer, Steven Donziger, directed the firm to ghostwrite a crucial damages assessment report for an ostensibly neutral and independent court-appointed expert, Richard Cabrera. They say that Donziger instructed them to keep Stratus's involvement in the writing secret even from the plaintiff team's then-communications director, Karen Hinton, as well as from Donziger's then-law associate, Andrew Wood.

Stratus, Beltman, and Maest reached a cooperation agreement with Chevron last month, finalized this week, that calls for the firm to make its experts available to give "truthful testimony" in exchange for Chevron's agreement to drop the three of them from a civil racketeering suit it filed in 2011 against them, Donziger, and several lead Ecuadorian lawyers in the case.

Attorney Craig Smyser of Houston, who represents the Ecuadorian plaintiffs team in the RICO case, says in a statement: "Chevron bullied Stratus until Stratus had no choice but to succumb: The firm was faced with financial extinction" from the RICO suit and its potential consequences to its government contracting business.

Smyser quotes language that an attorney then representing Stratus filed in court three months ago, stating: "Chevron knows that based on scientific data collected during the Lago Agrio litigation, including data collected by Chevron, Stratus actually found that contamination was present at every single well site and station that was sampled ... [causing] a huge amount of environmental damage costing immense sums to remediate."