An employee’s “intentional misconduct” led CHS Inc. to appear to be more profitable than it was, possibly for as long as four years, the company said this week.

The employee, who was fired after the misconduct was recently discovered, misvalued rail freight contracts at CHS, the giant agriculture co-op based in Inver Grove Heights. As a result, the company said it overstated its pretax profit by as much as $190 million over the past four fiscal years, or 12 percent of its $1.6 billion pretax profit in that time.

Financial statements in those years “should no longer be relied upon” and will have to be restated, CHS told investors in a filing with the Securities and Exchange Commission this week.

The company’s chief executive, Jay Debertin, sent a letter Friday to members of the co-op, chiefly farmers, to explain the trouble. “While the investigation is not yet complete, findings to date indicate there was no monetary loss to CHS,” Debertin said. “However, the company will incur additional costs related to this matter.”

The employee, who was not identified by CHS, also made “intentional misstatements” to PricewaterhouseCoopers, which audited the company’s results for the fiscal year ending in August 2017. A CHS spokeswoman declined to say whether legal action will be taken against the employee.

With revenue of nearly $32 billion, CHS just eclipsed 3M Co. in size last year and was the fifth-largest business in Minnesota after UnitedHealth Group, Cargill, Target and Best Buy.

Among its services that are tied to agriculture and energy, CHS contracts for space on large rail lines such as BNSF to move grain, oil and other commodities.

It uses much of that rail capacity itself, but it also resells space on trains to other companies in what’s called a secondary market.

The employee responsible for the accounting errors, according to the company, misstated the value and quantity of rail cars included in those contracts.

Accurate values for rail freight contracts are more difficult to verify than, say, the value of an oil contract or an everyday stock, said Haiwen Zhang, an accounting professor at the Carlson School of Management at the University of Minnesota. “You can’t just look it up on Yahoo Finance,” she said.

The valuations used by CHS for its rail freight contracts were likely based on quoted prices for similar contracts and could be subject to manipulation, Zhang said.

“Since the employee also overstated the quantity of the contract, overvaluation could easily happen,” she said. A “good internal control system should be able to capture both mistakes, though.”

CHS said in its regulatory filing that it is working to address failures in its internal controls of financial reporting.

The problem was discovered when executives at CHS noted potentially excessive valuations in the net derivative asset valuations of certain rail freight contracts associated with its grain marketing business.

The company hired Faegre Baker Daniels, the Minneapolis law firm, which then hired forensic accountants at Ernst & Young to investigate.

CHS estimated its pretax income over the last four years could be overstated by anywhere from $100 million to $190 million, and its net assets could be overstated by anywhere from $115 million to $220 million.

But the company’s analysis is ongoing, and the final adjustments to pretax income and net assets may differ from those estimates.

The company will try to file corrected statements for the fiscal year that ended in August 2018 by the end of November but could not assure that it would be done by then.

The value of CHS shares appeared relatively unaffected by the news.

In a week of volatile trading when broad market indexes fell 3 percent to 4 percent, CHS shares closed the week down less than a half-percent.