Self-adhesive stamps are expected to be on the market this summer, but U.S. Postal Service officials say they'll stick to their search for the perfect "lick and stick" seal.

Postal officials said last week they plan to test-market a stamp with a peel-off backing as part of their continuing effort to find out why some stamps stick and others don't.The Columbus-based Battelle Memorial Institute has been researching various moistenable adhesives since last July under a $700,000, 16-month contract with the post office.

It will be the second time the postal service has sold such stamps, said a Postal Service spokeswoman.