Oil prices fell to a three-and-a-half year low Monday, closing below $50 a barrel on the same day an influential economic group declared the U.S. economy has been in a recession for nearly a year.

Crude was already down 8% in midday trading after reports showed manufacturing activity in the U.S. was at a 26-year low and construction spending fell again in November.

Then the National Bureau of Economic Research said an array of economic indicators show that the recession began last December after 73 months of expansion which began in November 2001.

Crude oil for January delivery fell $5.10, or 9.4%, to $49.28 a barrel on the New York Mercantile Exchange.

Oil prices have fallen 66% since reaching a record $147.27 on July 11.

A global recession brought on by a collapse in housing prices and subsequent credit crisis has blunted demand for oil in the U.S., Europe and in developing nations such as India and China.

Analysts believe breaking the psychologically important $50 a barrel price could open the door to even further declines.

Also in play on Monday was news that the Organization of Petroleum Exporting Countries will not alter production amounts at least until its next meeting on Dec. 17.

OPEC, which accounts for about 40% of global supply, cut output by 1.5 million barrels a day in October, bringing total quota cuts to around 2 million barrels a day this year.

But the cuts have not helped stabilize prices, and crude oil has fallen another 26% since the last round of production cuts.

The Dow Jones Industrial Average was down more than 400 points on all the gloomy economic news.

Meanwhile, prices at the pump continued to fall, but at a slower rate. The price of a gallon fell half a cent overnight to $1.82, according to auto club AAA, the Oil Price Information Service and Wright Express. That’s less than half the $4 a gallon seen over the summer.

In other Nymex trading, gasoline futures tumbled 7.9 cents to $1.13 a gallon. Heating oil dropped 8.1 cents to $1.65 a gallon. Natural gas for January delivery, however, rose 13.7 cents to $6.65 per 1,000 cubic feet.