The performance of irrigation schemes around the world has been below expectations. The assessment of irrigation performance is an essential step towards improving agricultural water use. One of the primary performance indicators is the relative irrigation supply (RIS, the ratio between the amount of water delivered and the crop net irrigation requirements). This study presents a worldwide analysis of irrigation scheme performance by evaluating key attributes that influence the RIS. The analysis was based on a review of reports and scientific papers that yielded 264 cases belonging to 25 countries in six world regions. The database was subjected to two types of statistical analysis: k-means clustering and analysis of covariance (ANCOVA). The cluster grouped irrigation schemes which were characterized by low RIS and advanced irrigation technology. The ANCOVA showed that the RIS co-varied significantly with the variation in precipitation, delivery schedule, on-farm irrigation systems, distribution network, and region, but not with the crop. The ANCOVA also showed that modern pressurized on-farm irrigation systems and on-demand distribution systems significantly improve RIS. The ANCOVA general linear model had a good capacity to predict RIS with a coefficient of determination of R2 = 0.83. The first author acknowledges the financial support of the University of Costa Rica to carry out his doctoral degree at the University of Córdoba, Spain.