Fincance Ministry spokesman Juan Frances Escudero said "demand was very high. There was a lot of interest from investors at home and abroad."
He said the issue Tuesday was priced at mid-swaps plus 195 basis points and demand rose to euro13 billion.
Spanish financial daily Cinco Dias said the sale boosted trading on Madrid's Ibex stock exchange by more than 3 percentage points.
Spain, which is struggling to emerge from nearly two years of recession, is fighting speculation it will need a bailout to help it manage its debt.