Standard and Poor's has lowered the outlook for the world's top oil exporter Saudi Arabia to negative and downgraded its Gulf partners Oman and Bahrain on sliding oil prices.
But despite the large budget deficit planned by Riyadh for this year, the agency maintained its sovereign credit ratings for the kingdom, as well as neighbouring Abu Dhabi and Qatar, citing their "very strong fiscal positions."
"Given its high dependence on oil, Saudi Arabia's currently very strong fiscal position could weaken owing to the oil price decline," S&P said in a statement on Monday.
"The negative outlook reflects our view that Saudi Arabia's general government fiscal position is weakening," it said.
S&P lowered its outlook for Saudi Arabia from positive to stable in December citing similar reasons.
The agency has since further lowered its projections for world oil prices.
In December 2014, S&P expected benchmark Brent North Sea crude prices to average $80 per barrel in 2015 and $85 a barrel in 2015-2018.
"We now assume an average Brent oil price of $55 a barrel in 2015 and $70 a barrel in 2015-2018," it said.
Unlike Saudi Arabia, the neighbouring United Arab Emirates expects to balance its budget this year, and S&P maintained its "AA/A-1+" ratings and stable outlook for Abu Dhabi.
It said it expected the emirate, which accounts for 90 percent of UAE crude output, to remain prudent and flexible in its fiscal policy.
"But we also anticipate structural and institutional weaknesses to remain," it added.
Gas-rich Qatar has yet to unveil its budget for this year but S&P maintained its "AA/A-1+" sovereign credit ratings and stable outlook for the emirate.
The smallest Gulf producers, non-OPEC Bahrain and Oman, which lack the fiscal reserves of their wealthier Gulf partners, both saw their ratings downgraded one notch.
Bahrain's sovereign credit ratings were cut to "BBB-/A-3" from "BBB/A-2" and Oman's to "A-/A-2" from "A/A-1."
World oil prices plunged more than 50 percent last year and have since rebounded only feebly, amid forecasts of weak growth in key consumer countries and a continuing, if reduced, boost to supply from North American shale producers.
The International Monetary Fund estimated last month that the six Gulf Arab states -- which also include Kuwait -- would suffer $300 billion in lost revenues this year because of the price slump.