EARLIER this year it all looked so rosy. In April, just two years after Greece imposed the biggest sovereign-debt restructuring in history on its private creditors, it raised €3 billion ($4.2 billion at the time) in five-year bonds at a yield of less than 5%. In July its ten-year bonds were yielding less than 6% and their Spanish and Italian equivalents less than 3%, not far off Germany’s. The troubled economies of Europe’s “periphery” were beginning to turn around, it seemed, and the European Central Bank (ECB) would do whatever it took to keep the euro zone together.

That all went out the window in the global market sell-off of October 15th-16th. Yields on Greek government debt briefly exceeded 9%; the spread between yields on German government bonds and those of debt-addled euro-zone countries widened and lower-rated corporate-bond yields rose sharply too. Part of the rise might have been due to bond markets’ declining liquidity. At any rate, some ground has since been regained, with corporate bonds especially buoyed by the rumour (later denied) that the ECB was about to buy corporate debt as part of an asset-purchase scheme.

But worries that slow growth in the euro zone will be a serious drag on the world economy are increasing. Deflation, which makes debts harder to bear, has taken hold in the periphery, and threatens to afflict the euro zone as a whole. Faith that the ECB will be able to do much about either problem is declining. Against that background some euro-zone debt—both public and private—looks unsustainable.

Between 2007 and 2013 the ratio of government debt to GDP in the euro area rose from 66% to 93%. The spike was more dramatic in the periphery (see chart): in Greece the ratio increased to 175% and in Portugal it virtually doubled to 129%. High government debt itself does not necessarily crimp economic growth. But as bond yields rise, servicing that debt becomes difficult. Italy—with the third-largest stock of government debt in the world, much of it refinanced each year—is a particular concern. According to estimates from Moody’s, a rating agency, it will have to find around €470 billion of funding next year, worth nearly one-third of its GDP. The financing needs of other peripheral governments are not as drastic, but they are still high.
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The overhang of private-sector debt is also cause for concern. Overindebted firms struggle to grow and invest, while tying up scarce bank capital, which impedes lending to worthier borrowers. The picture is not uniformly grim. Despite Italy’s staggering government debt, its households owe less than Germany’s and its non-financial companies not much more. Spain’s private sector has deleveraged substantially over the past few years, as big recapitalisations have left its banks better able to withstand write-downs of bad loans.

But peripheral countries typically have a long tail of heavily indebted firms. In Portugal around a quarter of listed firms have debts of more than five times their earnings before interest, tax, amortisation and depreciation—the worst ratio in the periphery, points out Alberto Gallo of RBS, a bank. And the proportion of loans in default is still rising in Portugal, Italy and Greece, he says.

On October 26th the results of the ECB’s review of the books of big euro-zone banks will be released. They are expected to show few serious problems. Banks have been raising capital to be sure not to be found wanting. After it they may write down more bad loans rather than rolling them over. Another change is to corporate insolvency regimes, which typically make it harder to call in debts or seize collateral in the euro area than in America. All the peripheral countries have either reformed their laws or promised to do so, and the European Commission is pushing a common European standard.

Government debt looks more intractable, especially in light of the lacklustre growth and slide towards deflation that now seem entrenched. A recent analysis by Fitch, a rating agency, suggests that it will be very hard for any highly indebted euro-zone government to reduce its debt-to-GDP ratio by 20 percentage points over the next eight years, still less return it to its pre-crisis level.

Governments need to run primary (ie, before interest payments) surpluses in order to pay off existing debt. The IMF reckons that Italy will reach and maintain a primary surplus of nearly 5% of GDP by 2018, but is less sanguine about other euro-zone debtors. Tax rises and spending cuts are hard to implement. A study of 54 emerging and advanced economies, by Ugo Panizza of the Graduate Institute, Geneva and Barry Eichengreen of the University of California, Berkeley shows that large and sustained primary surpluses are extremely rare. People in the southern periphery are especially fed up with austerity, which has had a massive cost in terms of unemployment and living standards. More bad news, and the situation could look critical once again.