We use data envelopment analysis to measure the relative efficiency among Indonesia's provinces in using input to produce output over a 20-year period that includes the global economic crisis. We then employ the inequality decomposition technique of a Theil's second measure to explore the extent to which the efficiency factor contributes to interprovincial income inequality. Our efficiency analysis reveals that most Indonesian provinces improved their relative inefficiency considerably in both resource utilization and allocation. Moreover, the relative inefficiency became convergent across provinces for the period. However, several provinces with serious pure technical and scale inefficiencies still exist in 2010. The province of Yogyakarta critically underperformed in resource utilization, and Central Kalimantan and Papua operate at further suboptimum scales. The former needs to develop appropriate mechanisms to efficiently use its given resources, while the latter need to mitigate business-unfriendly regulations and deal with financial constraints. The inequality decomposition analysis shows that interprovincial convergence of inequality in overall technical inefficiency largely contributed to the reduction in income inequality. The convergence of inequality in resource utilization inefficiency had a greater impact on inequality convergence in overall technical inefficiency than in resource allocation inefficiency. In 2010, pure labor productivity became a substantial new factor in determining income inequality. Since this measure is affected by per capita physical and human capital and technology, the spatial allocation imbalance of these factors has become a new concern in Indonesia.