Interest on Spanish and Italian debt fell to record low on Monday while Portugal's continued to drop as investor concerns about the eurozone's former laggards eased.
Borrowing costs for southern European countries have fallen since the European Central Bank brought in unprecedented measures in June to help boost weak inflation in the bloc.
Investors have also been cheered by upbeat data, particularly in the bloc's fourth-largest economy Spain, which expanded at its strongest rate for six years in the second quarter.
"The fact that these rates continue to decline and there is no reversal shows that nobody sees issues that are likely to push yields higher," said Patrick Jacq, a bond strategist at BNP Paribas.
Spanish 10-year bonds sank to 2.488 percent, a record low for the secondary market where investors trade existing debt, down from 2.541 percent on Friday.
Italy's borrowing costs also touched a new low of 2.666 percent, down from 2.714 percent.
The improving sentiment marks a sharp turnaround from recent years when investors feared Spain and Italy could join Greece and Portugal in needing an international bailout.
Sentiment towards Portugal has also improved in recent weeks after its credit rating was upgraded by Moody's ratings agency thanks to its improving public finances.
Portugal, which exited its own 78-billion-euro ($105-billion) international bailout in May, has seen its borrowing costs fall as a result, sinking on Monday to 3.570 percent, from 3.640 percent Friday.
"The market accepts that the country is moving away from a critical situation," said Jacq.