Share prices in the energy-rich Gulf states nosedived Sunday following the sharp decline in oil prices and the expected rise in Iranian crude exports after the lifting of sanctions.
The plunge in the first day of trading in the Muslim week also follows heavy losses in global bourses on Friday, when Gulf exchanges were closed for the weekend.
The price of oil, which contributes more than 80 percent to Gulf states' revenues, shed more than 20 percent this year to drop below $30 a barrel. This follows a plunge of 65 percent in the past two years.
The return of Iran to the oil market will only worsen the production glut that has been the main reason for the oil price dive.
All seven Gulf bourses saw a wave of panicked sell-offs, sending indices to multi-year lows.
The Saudi Tadawul All-Shares Index, the largest Arab market, dived 6.5 percent to below 5,500-points just minutes after the start of trading. The level was last seen in early 2011.
The leading petrochemicals sector dipped 8.0 percent, while banks lost 5.3 percent.
Since the start of 2016, the TASI has dropped 21.1 percent, more than all of its losses last year.
The Qatar and Dubai bourses also dropped 6.0 percent at the opening before easing slightly.
The Dubai Financial Market was trading down 5.0 percent to below the 2,700-point mark. Blue chips properties giant Emaar and leading construction firm Arabtec dropped 5.3 percent and 7.0 percent.
The Qatar Exchange, the second largest in the Gulf after Saudi Arabia's, fluctuated sharply within minutes after opening. The bourse was trading down 5.6 percent below the 8,700-point level.
Since the beginning of this year, Dubai has dropped 15 percent and Qatar shed 17 percent.
The Abu Dhabi Securities Exchange also slumped 4.3 percent but remained above the 3,700-point mark. All sectors were down.
The Kuwait Stock Exchange dropped 3.2 percent to just above the 5,000-point mark, levels only seen in 2004.
The small market of Oman dropped 1.5 percent and Bahrain 0.3 percent.
Since the beginning of 2016, the seven stock markets have shed more than $130 billion of their market capitalization, which now stands at about $800 billion.
All Gulf stock exchanges ended 2015 in negative territory, led by Saudi Arabia, after the sharp decline in oil prices.