An independent audit of Spain's banks has found that they will need up to 62 billion euros in extra funding. The EU has already agreed to provide up to 100 billion euros.
Finance minister Luis De Guindos said Spain would officially ask for the aid in the coming days.
The estimates of extra funding came from audits by two companies: Oliver Wyman of the United States and Roland Berger of Germany.
Oliver Wyman estimated between 51 - 62 billion euros would be required, while Roland Berger estimated 51.8 billion euros.
They were asked to work out how much money the banks would need if the Spanish economy were to shrink 6.5% and house prices fall 60% from their peak.
Their research covered 14 banking groups that account for 90% of Spain's banking sector.
The figures were announced at a news conference by Bank of Spain deputy governor Fernando Restoy, who declined to comment on individual banks.
Meanwhile, the short-term cost of borrowing by Spain continues to rise.
Madrid on Thursday sold 2.2 billion euros of bonds repayable over two, three and five years.
It paid a yield of 6.07% on five year bonds, up from 4.96% in May and the highest in 16 years.