Energy shares were once against the biggest losers of the day in morning trading on Thursday, continuing a recent trend of weakness amid falling oil prices.

The S&P energy index .SPNY fell 1.5 percent and was the biggest decliner among the ten primary S&P 500 sectors. It has fallen almost 14 percent from a record high in late June, putting the sector well within correction territory, defined as a 10 percent decline from a peak.

Including Thursday's move, the index has posted declines of more than 1 percent on ten occasions since the start of September.

Crude oil CLc1 fell 0.9 percent to $86.55 per barrel, dropping to its lowest level since April 2013. From a closing high in September 2013, oil is down more than 21 percent, putting the commodity into bear market territory. Oil was pressured by a supply glut and concerns over global economic growth.

The Philadelphia SE Oil Service sector .OSX fell 2.6 percent. Among specific companies, Halliburton Co (HAL.N) fell 2.9 percent to $58.66 while Newfield Exploration Co (NFX.N) lost 4.1 percent to $32.44. Exxon Mobil (XOM.N) lost 1.2 percent to $93.49 and Chevron Corp (CVX.N) was down 1.6 percent to $116.08.

Index snapshot at 10:12 EDT:

* S&P 500 .SPX fell 12.22 points, or 0.62 percent.

* Nasdaq Comp .IXIC lost 32.93 points, or 0.74 percent.

* Dow industrials .DJI dropped 100.63 points, or 0.59 percent.

* Russell 2000 .TOY dropped 13.87 points, or 1.26 percent.

* S&P MidCap .IDX sank 13.68 points, or 1.01 percent.

* S&P SmallCap .SPCY lost 6.94 points, or 1.1 percent.