The proliferation of market-based public service delivery raises concerns whether the vulnerable are dully served and what mechanisms may facilitate to serve them well. Using the dimensional publicness theory, the present study examines how ownership, public funding, control and policy environments shape organizational offerings of special substance abuse treatment programs targeting at the vulnerable groups. The multi-level analyses indicate that public funding and control are two major policy mechanisms toward the realization of public outcomes, much more so that ownership. Policy environments exercise differential impacts on organizations, with a higher level of publicness in policy environments leading private organizations to offer more special programs for the vulnerable groups. Further analyses show that policy mechanisms take on different parameters in serving different vulnerable groups, calling for contingent understanding of the dimensional publicness theory and its possible application. The study concludes with the discussion of theoretical development and its policy implications in serving the vulnerable groups with substance abuse treatment demands.