By Ben Edwards and Josie Cox 

Some of the world's riskiest government borrowers are embarking on a last minute debt-raising spree before the markets shut for the winter break, extending a record-breaking year for so-called frontier bond sales.

Frontier market countries including Kenya, Ethiopia and Pakistan--each rated at least four notches below investment grade--all announced debt sale plans Tuesday, seeking to benefit from still relatively low interest rates and persistent investor demand for higher yielding debt. The window for issuing new debt generally closes in the middle of December for several weeks.

"If you wait until January, there's generally a lot of issuance so if you are a smaller borrower you might be concerned that you'd get swamped out," said Stuart Culverhouse, chief economist and head of research at Exotix, an investment banking brokerage that specializes in frontier markets.

So far this year, frontier borrowers including Kazakhstan, Ivory Coast and Vietnam have raised about $37 billion from selling bonds, roughly 50% more than in the whole of 2013 and the highest on record, according to data provider Dealogic.

Kenya is Tuesday seeking to increase the size of its debut dollar bonds it issued in June, following details that Ethiopia is poised to meet with investors ahead of its first-ever dollar bond sale. Pakistan is also Tuesday pressing ahead with plans to sell Islamic law bonds, which could be wrapped up as soon as Wednesday.

Demand is still looking good for this type of debt," said Kevin Daly, an emerging-market fund manager at Aberdeen Asset Management in London.

Mr. Daly said he is considering buying some of Kenya's bonds Tuesday and is planning to meet with officials from Ethiopia Wednesday.

African debt has performed strongly this year despite a minor blip last month, triggered by tumbling oil prices and concerns about the Ebola outbreak. On average, African government bonds yield 5.25%, roughly 0.75 percentage point lower than at the start of the year, according to a JPMorgan index. Yields fall when bond prices rise. That has lifted total returns--which include price changes and interest payments--to almost 12%.

Meantime, Pakistan's bonds yield 6.84% on average, about 1 percentage point lower than at the start of the year, according to a Markit index.

Bankers working on the Kenya deal are suggesting the bonds will price to yield in the area of 5.25% for the debt maturing in 2019 and around 6.125% for the debt maturing in 2024. Those bonds are currently trading at yields of about 5% and 5.8% respectively, according to Tradeweb. The original sale in June raised Kenya $2 billion, and was one of the largest first-time issues from an African nation.

Ethiopia's investor meetings are due to start Wednesday and conclude Dec. 3., according to a person familiar with the matter.

Pakistan's Sharia-compliant five-year bond--or sukuk--is being marketed at a yield in the area of 6.875%, according to a banker working on the sale.

The deal follows a number of other countries such as South Africa and the U.K. that have issued sukuk in recent months. Tunisia and Kenya are also both eyeing that market, investors say.

Sukuk paper trades, clears, settles and is rated in a similar way to non-Sharia compliant bonds, but is structured to abide by Islamic law. This means it is usually backed by assets or cash flows, as the religion forbids interest payments. As a result, sukuk issuers are able to tap a different pool of investors than with more conventional bonds.

Pakistan's sukuk is expected to be rated Caa1 by Moody's Investors Service, seven levels below investment grade.

Ethiopia in May was handed credit ratings from Moody's, Standard & Poor's Corp. and Fitch Ratings in preparation for a potential deal. The country is rated B1 by Moody's and B by S&P and Fitch, four and five levels below investment grade respectively. Moody's said at the time that its rating reflects Ethiopia's strong economic growth over the past decade.

Kenya is rated B1 by Moody's and B+ by S&P and Fitch.

Barclays, J.P. Morgan Chase & Co. and Standard Chartered are managing Kenya's debt sale Tuesday.

Citigroup, Deutsche Bank, Dubai Islamic Bank and Standard Chartered are running the Pakistan sukuk sale.

Deutsche Bank and J.P. Morgan are organizing the Ethiopia bond roadshow.

Write to Ben Edwards at ben.edwards@wsj.com and Josie Cox at josie.cox@wsj.com

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