Midstream oil and gas firms in South-South Nigeria face a persistent paradox of resource wealth coexisting with weak organizational sustainability. Chronic oil spills, gas flaring, operational inefficiencies, and fractured social contracts with host communities collectively underscore the urgency of identifying strategic antecedents of sustainable performance in this sector. This study investigated the relationship between ambidexterity and organisational sustainability of midstream oil and gas firms in South-South, Nigeria, with information technology infrastructure as a moderating variable. The proxies of ambidexterity were exploitative ambidexterity and explorative ambidexterity, while the proxies of organisational sustainability were environmental sustainability, economic sustainability, and social sustainability. The study was anchored on contingency theory, dynamic capabilities theory, the moral responsibility theory of corporate sustainability, and the technology-organization-environment framework. Underpinned by the positivist philosophical paradigm, a cross-sectional survey design was adopted, with primary data collected from 274 middle-to-top management staff drawn from 56 midstream oil and gas firms registered with the Petroleum Technology Association of Nigeria in South-South, Nigeria, Seven null hypotheses were tested at the 0.05 level of significance using Partial Least Squares-Structural Equation Modelling via SmartPLS 4.1.1.7. The findings revealed that exploitative ambidexterity has a strong, positive, and significant relationship with both environmental sustainability and economic sustainability, but a weak, non-significant relationship with social sustainability. Explorative ambidexterity exerted a strong, positive, and highly significant effect on economic sustainability and social sustainability, but a negligible, non-significant effect on environmental sustainability. Information technology infrastructure exerted no significant moderation effect. The study recommended that management teams, operations directors, and HSE officers should  institutionalize exploitative ambidexterity as a core environmental sustainability strategy by conducting regular internal environmental performance audits, and investing in incremental improvements to pipeline integrity monitoring systems, gas flaring reduction technologies, and spill containment infrastructure.