For European banks, it's a headache that just won't go away: the 944 billion euros (US$1.17 trillion) of non-performing loans that are weighing down their balance sheets.

Economists say the pile of past-due and delinquent debt makes it harder for banks to lend more money, hurting their earnings. European authorities are prodding lenders to sell or wind down non-performing credit, but they're split on how to tackle the issue, and some investors are disappointed by the pace of progress.

There are various ways of calculating soured loans. The European Central Bank (ECB) advises that non-performing asset indicators should be interpreted with caution because the definition of impaired assets and loss provision differ between countries. The data used below refers to domestic banking groups and stand-alone banks only, and excludes foreign subsidiaries and controlled branches.