Nigeria’s return to democratic governance in 1999 coincided with a deepening reliance on crude oil as the dominant source of government revenue, foreign exchange earnings, and export income. By the early 2000s, oil accounted for over 70% of government revenue and more than 90% of export earnings, establishing a structurally dependent fiscal system that weakened diversification and shaped governance outcomes. This study examines how oil dependence influenced governance performance in Nigeria between 1999 and 2025, with emphasis on institutional capacity, fiscal management, and accountability mechanisms. A qualitative research design was adopted using secondary data from Central Bank of Nigeria reports, NEITI audits, policy documents, and peer-reviewed literature. Thematic content analysis was used to examine patterns across administrations from Obasanjo to Tinubu. Findings show that despite successive reforms such as EFCC, NEEDS, ERGP, and the Petroleum Industry Act, oil dependency remained persistently high at 60–80% of federal revenue, contributing to fiscal instability, corruption risks, revenue volatility, and weak institutional performance. The study is anchored on Resource Curse Theory, which explains how resource abundance can undermine governance quality through rent-seeking behaviour, weak accountability structures, and overreliance on extractive revenues. Across administrations, global oil price fluctuations consistently triggered budget deficits, increased borrowing, and underinvestment in productive sectors. The study concludes that oil dependence has significantly constrained governance effectiveness in Nigeria between 1999 and 2025. It recommends economic diversification, strengthening of regulatory institutions, improved transparency in oil revenue management, and enforcement of fiscal responsibility frameworks to reduce vulnerability to oil shocks and enhance sustainable development. Keywords: Oil dependence; Governance; Resource Curse Theory; Fiscal instability; Institutional accountability
ELEYI et al. (Sat,) studied this question.