The Saudi Tadawul All-Shares Index, the largest in the Arab world, slid 3.3 percent by mid-session to 9,460.41 points -- the lowest level since March -- a day after shedding 3.5 percent.
Losses were seen across all 15 sectors with the key petrochemicals industry losing 3.9 percent.
Dubai Financial Market Index slid 3.26 percent to close at 4,400.80 points.
Market leader Emaar Properties fell 3.94 percent and construction giant Arabtec tumbled 5.7 percent.
Neighbouring Abu Dhabi Securities Exchange closed down 2.5 percent at 4,825.51 points, while Qatar Exchange lost 2.0 percent to end the day at 13,528.67 points.
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Kuwait Stock Exchange fell 1.4 percent to 7,193.42 points while Oman dropped 1.3 percent and Bahrain slipped 0.2 percent.
Gulf shares have been fluctuating sharply because of the slide in oil prices, which have shed about 30 percent of their value since June.
Oil prices extended losses in Asian trading on Wednesday as traders looked ahead to the release of the latest US supply report and sweated over price cuts by Saudi Arabia.
US benchmark West Texas Intermediate (WTI) for December delivery fell seven cents to $77.12 while Brent crude for December declined 33 cents to $82.49 in afternoon trade.
WTI had dropped $1.59 in New York late Tuesday to hit its lowest closing point since October 2011, as dealers continued to digest Saudi Arabia's move to cut its prices for crude sold to the US markets.
Brent fell $1.96 in London to its lowest close since October 2010.