Flame spreading along the pool surface of O/W (oil-in-water) emulsion type gelled hydrocarbon fuels with high internal phase ratios have been investigated from the standpoint of spilled-fuel fire prevention. Aspects of flame spreading and temperature field in the vicinity of the spreading flame front were observed and measured by 16 mm movie pictures, interferometry and thermocouples. It was found that a thin liquid layer flow ahead of and below the flame exists if the neat hydrocarbon fuel has a flash point higher than the ambient temperature and or has considerably different flash and fire points. No such liquid layer flow can be observed if the neat fuel has a flash point below the ambient temperature and consists of a single component. Whether such a liquid layer flow exists or not would have a large influence on such aspects of flame spreading as velocity, direction and steadiness. The influences of the initial temperature and the oil content of O/W emulsion on flame spreading velocity were investigated. Characteristics of flame spreading upward and downward along an inclined pool were also examined by altering the inclination angle and comparing results with those for a horizontal pool.