After the coal giant applied for bankruptcy protection earlier this week, shares which traded in 2008 at about $US80 were rendered essentially worthless.

Patriot was delisted from the New York Stock Exchange on Wednesday.

The investigation by securities arbitration law firm Klayman & Toskes regards Patriot shareholders with high concentration investments which experienced a loss of $750,000 or more.

The investigation is focusing on mismanagement of client portfolios given the fact that there were risk management strategies that would have protected the value of the concentrated portfolio.

Klayman & Toskes said a hedge strategy known as a “zero cost” collar, would have created a range of value that the portfolio would have maintained irrespective of the fluctuation and direction of the underlining stock price.

According to the firm, failure to use risk management strategies or hedge the value of a concentrated portfolio directly exposes an investor’s concentrated position to the fluctuations in volatile securities markets.

Patriot’s chapter 11 filing was made well after the US stock market closed Monday, although earlier speculation around the filing sent the company’s stock into 72% free-fall to 61c.