Brent crude oil has fallen below US$50, marking its lowest level since early 2009. It is now at a six-year low.

The price of a barrel of the North Sea benchmark dropped by 5.5 percent, bring the value to US$47.36. U.S. crude oil is similarly at its lowest level since 2009, down by 5 percent to US$45.90 a barrel.

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United States stocks fell for a second straight session on Monday. The drop was led by the sharp decline seen in energy shares brought about by these falling oil prices. Concern is brewing for corporate earnings season.

Goldman Sachs said the price would stay near US$40 for the first half of the year. The firm said investment in the U.S. shale gas industry would be help up.

CMC Markets analyst Michael Hewson indicates that with OPEC not doing anything about over-production, it seems likely that the price will decline towards US$40 in the coming weeks.

The current price is now more than half than it once was since June. At the time, a price for a barrel was US$110.

The actions of North American shale companies helped to depress prices as supply of oil and gas has increased.

Slowing global economic demand and a rising dollar against other currencies is also undermining the price of oil.

As such, profit forecasts for S&P 500 energy companies have dropped sharply in recent months. Fourth quarter earnings for the sector are now expected to have declined 21.1 percent from a year ago according to Thomson Reuters data.

"Crude oil is heading down again here. That's sent us into negative territory again," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York. "There's a lot of confusion and concern about the impact of oil prices."

Ghriskey adds that the one thing everybody is currently concerned with is what managements are going to say about crude oil and about global economies.

TagsBrent, crude oil, opec, U.S. economy, oil and gas industry