Regulators launched one of the biggest ever crackdowns on oil price manipulation on Tuesday, suing two well-known traders and two trading firms owned by Norwegian billionaire John Fredriksen for allegedly making $50 million by squeezing markets in 2008.

The Commodity Futures Trading Commission (CFTC) said traders James Dyer of Oklahoma's Parnon Energy, and Nick Wildgoose of Europe-based Arcadia Energy, amassed large physical positions at a key U.S. trading hub to create the impression of tight supplies that would boost oil prices.

Read the complete Reuters story, “U.S. sues big oil traders for 2008 manipulation.