Investors currently think that 15-year collateral has become significantly more efficient in refinancing relative to its 30-year counterparts, causing spreads to widen. However, in spite of this development, 15-year product continues to offer good call protection, analysts said.

"Over the last month 15-year OAS's have widened dramatically versus their 30-year counterparts and are currently at their widest levels in over four years," reported Bear Stearns in recent research.

Subscribe Now

Access to a full range of industry content, analysis and expert commentary.

30-Day Free Trial

No credit card required. Access coverage of the securitization marketplace, including breaking news updated throughout the day.