Peatlands have been artificially drained and degraded over 100s of years and have released huge amounts of carbon dioxide (CO2) as a result. In organic grassland soils, raising the water table to prevent such emissions is being proposed to meet national greenhouse gas emission targets for the land use sector. At present, all of these soils (335,000 ha) are assumed to be drained (as no information has been available on their drainage status) within national emission inventory reporting and are therefore responsible for significant emissions (8–9 million tonnes CO2-equivalent annually). The objective of the present study was to collate studies relating to the drainage status of peat soils in Ireland to present alternative scenarios with regard to actual drainage status of organic soils and their estimated emissions. From a drainage design perspective, evidence suggests that relatively small proportions of the grassland peat area was drained effectively using optimal in-field drain spacings required to control the water table at 0.4–0.5 m. Open drains excavated on such soils have limited capacity to laterally control the water table depth beyond short distances. Furthermore, the lack of long-term routine maintenance post installation ensures the redundancy of many drainage systems over time. New drainage installations are therefore likely replacing existing infrastructure and not necessarily increasing the drained area at any given time. This evidence supports literature from the 1980s which state that relatively low proportions of the grassland peat area has been subjected to effective drainage. Scenario testing results showed that likely emissions from the most probable scenario (with total area drained equating to 90,000–120,000 ha) are 3.6–4.7 million tonnes CO2-equivalent, approximately 40–53% of current national emission inventory estimates. The incorporation of such a refinement into the national inventory could offer a significant reduction in estimated GHG emissions from the grassland land use sector in national emission inventory reporting. •In Ireland, it is assumed that all 335,000 ha of mapped grassland peat soils are drained.•This estimate results in assumed GHG emissions of 8–9 million tonnes CO2-e per year.•The proportion of grassland peat soils actually drained is much lower than the current estimate.•Evidence shows that drainage works on peat soils are limited in extent and effectiveness.•Scenarios based on updated drainage status result in emission savings of up to 60%.