Research on incarcerated men indicates low PrEP access even though HIV disproportionately affects them. Intersecting attributes - urban, incarcerated, Black, heterosexual men with substance use diagnoses (SUDs) - improves the odds of HIV transmission/acquisition. It is crucial to determine, among "key populations," who might be eligible to take PrEP. PrEP eligibility criteria have been used inconsistently in research. This exploratory, quantitative, study uses criteria from the United States Centers for Disease Control and Prevention to determine eligibility: HIV-negative test and sexually active plus a sexual partner living with HIV and/or diagnosed with an STI and/or inconsistent or no condom use for intercourse. We found a considerable percentage (