Brent crude oil falls more than $1 to 4-year low of $81.23

The US dollar hit a 7-year high against the yen and was up 0.2 percent on the day against a basket of currencies.

Production from shale oil fields in the United States showed no signs of slowing despite falling prices, the Energy Information Administration said in a forecast on Monday.

US crude futures fell by 98 cents to an intraday low of $76.42.