DURHAM, England — THIS summer, disgruntled Saudis took their grievances online in droves, complaining of ever-growing inequality, rising poverty, corruption and unemployment. Their Twitter campaign became one of the world’s highest trending topics. It caused great alarm within elite circles in Saudi Arabia and sent ripples throughout the region. The rallying cry that “salaries are not enough” helped to prove that the monarchy’s social contract with its people is now publicly coming unstuck, and on a significant scale.

Many experts believe that the Gulf states have survived the Arab Spring because they are different. After all, they’ve weathered numerous past storms — from the Arab nationalist revolutions of the 1950s and ’60s to Saddam Hussein’s 1990 invasion of Kuwait to an Al Qaeda terror campaign in 2003.

But they are not different in any fundamental way. They have simply bought time with petrodollars. And that time is running out.

The sheiks of the Persian Gulf might not face the fate of Col. Muammar el-Qaddafi of Libya or Hosni Mubarak of Egypt next year, but the system they have created is untenable in the longer term and it could come apart even sooner than many believe.

Saudi Arabia is the kingpin of the six Gulf monarchies, so its internal stability is crucial for the region, especially since so much attention has now been turned toward these anachronistic political systems in the wake of the 2011 uprisings.

Although it’s never healthy to treat any state as exceptional, Saudi Arabia is indeed a bit different from its neighbors. Unlike Mr. Mubarak or Colonel Qaddafi, Saudi Arabia’s octogenarian king, Abdullah bin Abdulaziz al-Saud, has had the oil-financed means to buy off protesters. He has managed to calm the anger that has flared up in his backyard by ramping up subsidies, dramatically increasing public-sector employment and announcing huge and unprecedented government spending programs. So far, this has been a fast and effective way to keep the masses off the streets.

But this is not evidence of royal resilience, as some Western diplomats and academics have argued. On the contrary, Saudi Arabia’s resource-fueled strategy is a response to rising discontent across the region, and it is driven by a deep-seated fear that restive populations across the Arab world could incite unrest closer to home.

Moreover, spending for stability’s sake in Saudi Arabia and the other Gulf monarchies will necessarily be quite short-lived. The kingdom pledged a record-breaking $500 billion for “welfare” this year — most to be spent on social security subsidies and new public sector jobs.

Such vast wealth distribution can’t be kept going for much longer. That level of public expenditure is not sustainable and it flies in the face of decades of efforts to promote better fiscal accountability in the kingdom and wean the population off handouts and public-sector entitlement.

Thus, on top of declining oil reserves, rapidly rising domestic energy consumption and increasing energy-supply diversification among its allies, the kingdom’s spiraling spending is also fast raising the break-even oil price for Saudi Arabia and all five of the other Gulf monarchies; in other words, the price of a barrel of oil that these states need in order to balance their books is getting higher and higher. In Bahrain it’s now over $115 (far higher than yesterday’s price of around $102) while in Oman it’s up to $104.

In Bahrain and Oman, dependency on a high oil price is becoming perilous, while in the small oil-rich monarchies, ministers are starting to talk openly of a break-even price. That would have been unimaginable just a few years ago. In early October, even Kuwait received a warning from the International Monetary Fund. It was told it had to rein in its spending on welfare and public sector jobs and boost non-oil income as soon as possible.

Much worse for the Gulf’s ruling families than the looming economic crisis is the fact that their repressive response to protests is now starting to have a demonstrable impact on their legitimacy as carefully honed social contracts begin to fray.

The initial slew of arrests and small number of deaths in the first half of 2011 have since been dwarfed by huge crackdowns. Bahrain and Saudi Arabia have been the most brutal, with dozens dead in Bahrain and about 18 killed in Saudi Arabia. All the neighboring states have taken many political prisoners. Last year, Qatar even sentenced a poet critical of autocracies to life imprisonment, later commuted to 15 years.

The author of “After the Sheikhs: The Coming Collapse of the Gulf Monarchies,” who teaches Middle East politics at Durham University.