This systematic review examines the abundance of microplastics in the world's five oceans, focusing on surface waters. The study uses data from 73 primary studies conducted since 2010, following OSPAR guidelines to monitor and harmonize marine debris. The results show significant differences in microplastic abundance and distribution across the oceans, with the Atlantic Ocean having the highest mean concentration (4.98 items/m³) and the Southern Ocean the lowest (0.04 items/m³). The overall concentration of microplastics ranged from 0.002 to 62.50 items/m³, with a mean abundance of 2.76 items/m³. The study highlights the need for standardized sampling, separation, and identification methods to improve data comparability and inform effective mitigation strategies for reducing marine plastic pollution. The findings also indicate that secondary microplastics, primarily from single-use plastics and fishing gear, are more prevalent than primary microplastics from industrial sources. The analysis of physical properties, such as shape, color, and polymer types, further supports the understanding of microplastic sources and their environmental impacts.This systematic review examines the abundance of microplastics in the world's five oceans, focusing on surface waters. The study uses data from 73 primary studies conducted since 2010, following OSPAR guidelines to monitor and harmonize marine debris. The results show significant differences in microplastic abundance and distribution across the oceans, with the Atlantic Ocean having the highest mean concentration (4.98 items/m³) and the Southern Ocean the lowest (0.04 items/m³). The overall concentration of microplastics ranged from 0.002 to 62.50 items/m³, with a mean abundance of 2.76 items/m³. The study highlights the need for standardized sampling, separation, and identification methods to improve data comparability and inform effective mitigation strategies for reducing marine plastic pollution. The findings also indicate that secondary microplastics, primarily from single-use plastics and fishing gear, are more prevalent than primary microplastics from industrial sources. The analysis of physical properties, such as shape, color, and polymer types, further supports the understanding of microplastic sources and their environmental impacts.