The technology of underground coal gasification to produce synthesis gas requires a flare to dispose of vented surplus gas. Since any coal seam will contain chlorine, there is the potential to produce dioxins (PCDD/F) in the flare flame, provided that chlorinated products are released during the gasification reactions. Because of the sulphur present in coals, it is unlikely that significant amounts of heterogeneous (solid phase) PCDD/F will form. Using an established model for dioxin formation, an estimate is made of the likely amount of homogeneous (gas phase) PCDD/F generated in the flame. The result suggests that any release to air will be well below international regulatory limits.