About 200 workers at two refineries staged demonstrations on Sunday, demanding higher wages, as a series of concessions by Oman's veteran ruler Sultan Qaboos bin Said have failed to quell discontent and unrest.
The protesters, along with those working in an oil field who went on strike last week, have complained that they are among the least-paid oil workers in the Gulf.
"We want higher pay, better pension, training, regular promotions and more Omanis in the management team," Mohamed Al Harthi, one of the protesters at the Muscat refinery, said.
The normally tranquil oil-producing nation at the mouth of the Gulf was stunned by protests last month that left at least one person dead in the industrial city of Sohar.
Oman produces about 800,000 barrels per day of oil, which accounts for more than 70 percent of the sultanate's income.
The two affected refineries are the Muscat refinery, with an output of 85,000 barrels per day, and the Sohar refinery, producing 120,000 barrels per day.
The government has already declared it would double monthly welfare payments and increase pension benefits for citizens.