By Jeannette Neumann and Christopher Bjork

MADRID--Small Spanish lender Liberbank SA (LBK.MC) was the only one of 16 lenders from the country to fail a balance-sheet exam by European regulators.

The bank had a capital shortfall of 32.2 million euros ($40.8 million) as of Dec. 2013, but the lender has addressed that capital deficit by raising EUR636.7 million through to September 2014, the European Central Bank said in an analysis published Sunday.

The European Central Bank said that its asset quality review showed that Banco Santander SA (SAN), the eurozone's largest bank by market value, had a core capital buffer of 10.34%. Lenders needed a buffer of above 8% of risk-weighted assets to pass the test.

In the "adverse" scenario, which tests the strength of banks' balance sheets amid a hypothetical deteriorating economic environment, Santander had an 8.95% capital ratio, the ECB said. Banks had to maintain a capital buffer of at least 5.5% in the adverse scenario.

For Spain, the adverse scenario included a significant drop in home prices through 2016 as well as a contraction of the economy this year and next, with growth of only 0.1% in 2016.

Banco Bilbao Vizcaya Argentaria SA (BBVA), Spain's second-largest bank by market value, had a core capital buffer of 8.97% under the worst-case scenario, while La Caixa, the majority owner of Caixabank SA (CAIXY), the country's third-largest bank, was 9.25%, the ECB said.

The ECB said its asset quality review showed that BBVA had a core capital ratio of 10.54%, while La Caixa had a 10.24% ratio.

Spanish bank executives, cabinet ministers and the country's central bank have said in recent months that they expected Spain's lenders to perform well on the balance sheet tests because lenders already underwent similar exams two years ago.

In 2012, Spain requested EUR41 billion from the European Union to bail out several regional savings banks, known as cajas in Spanish, which faced ballooning losses as real-estate developers stopped paying back loans issued during the country's building boom.

A condition of the bailout funds was a deep-dive look at Spanish banks' books. Oliver Wyman, a consultancy group, said in September 2012 that Spain's lenders had a capital deficit of EUR53.7 billion. Spain ended up borrowing EUR41 billion since some banks managed to raise capital from investors.

Write to Jeannette Neumann and Christopher Bjork at jeanette.neumann@wsj.com

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