Transient experiments with liquefied binary mixtures of methane-ethane and methane-propane boiling on water, show great differences in the boiling characteristics compared to pure methane. The high initial boil-off rates observed in some of the experiments, are believed to occur due to breakdown of film boiling while the water surface has a higher temperature than the superheat limit of the cryogenic liquid. The high initial bail-off rates were most profound in the methane-rich mixtures, comparable to commercial liquefied natural gas (LNG). These findings may have significance to the way heat transfer is implemented in the models describing rapid phase transitions (RPT) in the LNG-water system.