By Emese Bartha 

Portugal and Ireland, countries that have weaned themselves off international financial aid, are making new forays into capital markets this week.

Portugal launched a $4.5 billion, 10-year U.S. dollar-denominated bond via a syndicate of banks Wednesday, in a fresh sign of smooth and steady market access following its recent exit from a three-year bailout program. The total order book was in excess of $10 billion for the October 2024-dated bond, whose initial price guidance of 265 basis points above Treasurys was tightened to 260 basis points above Treasurys, one of the lead managers said. The transaction was lead managed by Barclays, Danske Bank, HSBC and Société Générale CIB.

This dollar issuance was expected by markets after Joao Moreira Rato, president of Portugal's debt agency IGCP, told The Wall Street Journal last week that the country was considering selling dollar-denominated bonds for the first time in four years. Mr. Rato said the issuance in dollars was aimed at diversifying Portugal's investor base.

Portugal exited its EUR78 billion ($106.8 billion) three-year bailout in May without asking for a precautionary credit line, and ratings firms have praised the country's achievements in fiscal consolidation. On May 9, Moody's Investors Service raised Portugal's rating to Ba2, or two levels into junk, from three levels, citing improved economic and market conditions. On the same day, Standard & Poor's Ratings Services' revised Portugal's outlook to stable from negative, and kept the country's rating at BB, also two levels into junk.

Ireland, which left its EUR67.5 billion bailout last December, meanwhile reduced the amount of redemptions it will have to pay back to investors in 2016 by slightly more than EUR2 billion through two operations--an outright buyback of its 4.60% April 2016 bond, and an exchange of the same 2016-dated bond for the 3.90% 2023 bond. The exchange operation was done on a two for one nominal basis--one 2023-dated bond sold for two 2016-dated bonds bought back.

As a result of the buyback and switch operations, a nominal EUR2.037 billion of the 2016-dated bond has been canceled, which in turn reduces its amount outstanding to EUR8.132 billion from EUR10.169 billion, Ireland's National Treasury Management Agency said.

Portuguese and Irish government bonds are in demand as investors are attracted by their relatively high yields in the current record low interest rate environment in the euro zone.

Portugal's 10-year euro-denominated bond yield is currently trading at around 3.62%, compared with levels around 6% at the beginning of the year. Irish 10-year bonds are trading at 2.40%, down from around 3.42% at the beginning of the year. By comparison, 10-year German Bunds, Europe's benchmark, are trading at around 1.29%.

Write to Emese Bartha at emese.bartha@wsj.com