The Reuters story on Constellation Energy's stock plunge is better. But it doesn't make sense that increased collateral for a multi-step bond downgrade that hasn't happened yet would bang the stock that bad. Is the energy bubble collapsing faster than anybody expected?

NEW YORK (Reuters) - Shares in Constellation Energy Group (CEG.N: Quote, Profile, Research) tumbled nearly 18 percent on Tuesday to their lowest level in almost two years after the power producer said a credit rating downgrade could force it to post billions of dollars in extra collateral.

Constellation said in a quarterly report with the U.S. Securities and Exchange Commission late on Monday that it had underestimated its collateral liabilities by $1.6 billion in the event its debt rating was cut three notches.

High volatility in fuel and electricity prices have increased the risk of a downgrade, and the company could be forced to post $3.37 billion in collateral to cover those contracts if its debt is downgraded three levels.

One analyst said that disclosure coupled with ongoing concerns about the transparency around the company's cash flows were worrying investors.