Foreign financial firms have sold $36.4 billion of investment-grade bonds in the U.S. so far in 2011, the most ever recorded in the first two weeks of any year since at least 1995, according to data provider Dealogic.

The so-called Yankee bonds--dollar-denominated debt sold in the U.S. by firms based outside the country--have come in 53 separate offerings, a 112% jump on last year's 25 deals up to this point, Dealogic added.

Including issuers other than banks, Yankee high-grade debt issuance in the U.S. totals $45.3 billion so far this year, accounting for more than 70% of the U.S. investment-grade bonds marketed overall. Financial institutions accounted for 81% of all Yankee high-grade bonds in the year to date.

One explanation for the surge of overseas issuers is the attractiveness of selling debt in dollars and swapping the cash flows back into euros, instead of selling debt directly in Europe, according to credit strategists at Barclays Capital.

In a market commentary Friday, the strategists said it was costlier for European firms to issue debt in their own markets because of the "relatively higher risk aversion" among investors stemming from the region's sovereign debt crisis.

The euro/dollar cross-currency basis swap spread--a measure of how much it costs to exchange cash flows in the two currencies--is now minus-26 basis points for a five-year swap. That means a European bank needing five-year funding in euros would save 0.26% on every dollar sold and swapped back in order to create the synthetic funding in euros, compared with what it would cost to issue in euros.

From 2000 to early 2008, that five-year basis swap spread was close to zero, so the differential is noteworthy even though the spread was even more negative during the financial crisis, Barclays added.

In the last two weeks, Australia & New Zealand Banking Group Ltd. (ANZBZ, ANZ.NZ, ANZ.AU) priced $3 billion of bonds in the U.S., Rabobank Nederland sold $2.75 billion, Lloyds TSB Bank PLC (LYG, LLOY.LN) sold $4.75 billion and HSBC Bank PLC (HBC) sold $4 billion.

-By Katy Burne, Dow Jones Newswires; 212-416-3084; katy.burne@dowjones.com