(Bloomberg) -- Alphabet Inc. is proposing to tap the bond market at rock bottom yields, in a rare debt sale that will help fund sustainability projects.

The parent company of Google may sell debt in six parts, according to a person with knowledge of the matter. The longest security, a 40-year bond, may yield between 1.25 and 1.3 percentage points above Treasuries, the person said, asking not to be identified as the details are private.

Alphabet has only borrowed in the U.S. investment-grade market a handful of times, with the last issue four years ago. It was cheap to sell bonds then, and could be even more of a steal now -- the company may pay just 40 basis points over Treasuries to borrow for five years, the person familiar said. Amazon.com Inc. initially marketed a similar range for a debt offering in June, which ended up pricing at a spread of 25 basis points.

Google has been expanding its use of sustainable energy, touting its carbon-neutral status for over a decade. It’s one of the world’s largest corporate buyers of renewable power.

More broadly, sustainable debt issuance has skyrocketed in the pandemic, most notably via social bond sales. Supply will almost double this year compared to last as more borrowers raise debt to respond to the humanitarian crisis presented by Covid-19, according to HSBC Holdings Plc.

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