Abstract
This article examines oblast-level electoral competition in Ukraine between 2010 and 2020 during decentralization reform. Using an adapted Vanhanen Index combining contestation against the national ruling party or governing coalition with electoral turnout, and applying linear mixed-effects modeling to an original regional dataset, the study identifies a nonlinear trajectory. The index declined significantly in 2015 relative to 2010 and recovered only partially by 2020. Regional variation also compressed sharply in 2015 and partly reemerged in 2020. The findings suggest that oblast level electoral dynamics reflected incomplete decentralization, changing national ruling-party dynamics, party-system realignment, war, and regional legacies.