Binding Commitments and Credit Spreads in Sustainability-Linked Bonds

Sustainability-linked bonds (SLBs) embed sustainability commitments directly into debt contracts, but the credibility of these commitments depends on how penalties, reporting obligations, and verification requirements are written and enforced. We construct bond-level measures of contractual enforceability and target precision from SLB frameworks, prospectuses, and performance-target documentation for 915 SLBs, and link them to secondary-market Z-spreads and to matched conventional bonds from the same issuer or corporate parent. Three findings emerge. First, the basic contractual architecture has become nearly universal: 92% of SLBs contain penalty-activation, reporting, and external-assurance provisions. Second, the full-document enforceability score is negatively associated with absolute SLB spreads after controlling for month and currency, although the association is sensitive to issuer controls. The contractual enforceability index is imprecisely related to absolute spreads, while SLB spreads net of matched same-issuer or same-parent conventional-bond spreads are 3.7 to 10.0 basis points lower per standard deviation of this index. These matched estimates are marginally precise and weaken under stricter matching. Third, spread reactions around individual disclosure and non-disclosure events are limited and heterogeneous. The evidence is consistent with credit markets valuing contractual credibility, but it does not establish a causal effect on financing costs.