Investors closed positions on the Abu Dhabi Securities Exchange (ADX) and the Dubai Financial Market (DFM) as oil prices declined below US$84.
Abu Dhabi National Energy, also known as Taqa, lost 0.6 per cent to Dh1.20. The ADX General Index closed down 0.3 per cent at 2,534.70 points.
West Texas Intermediate light sweet crude for November delivery dropped 0.9 per per cent to $83.65 a barrel. Members of the GCC supply about a fifth of the world's oil.
Traders were cautious and looked for developments on Europe's debt crisis.
"Investors are taking a wait-and-see approach before building positions again," said Nabil Farhat, a partner at Al Fajer Securities, a brokerage based in Abu Dhabi.
In Dubai, the bellwether Emaar Properties lost 1.4 per cent to Dh2.73 a share. Arabtec Holding was down 2.2 per cent to Dh1.33.
Dubai's main benchmark, the DFM General Index, was down 0.6 per cent to 1,438.41 points.
Elsewhere in the region: Kuwait's index was little changed at 5,849.10 points; Bahrain's measure lost 1.4 per cent to 1,183.25 points; Oman's index declined 0.6 per cent to 5,611.71 points; and Qatar's benchmark was little changed at 8,422.25 points.
The Saudi Tadawul ended its trading week down 0.2 per cent to 6,112.37.