the present invention relates to an improved explosive composition . more particularly , the invention relates to a water - in - oil emulsion explosive having improved stability and a lower viscosity . the term &# 34 ; water - in - oil &# 34 ; means a dispersion of droplets of an aqueous solution or water - miscible melt in an oil or water - immiscible organic substance . the term &# 34 ; explosive &# 34 ; means both cap - sensitive explosives and noncap - sensitive explosives commonly referred to as blasting agents . the water - in - oil emulsion explosives of this invention contain a water - immiscible organic fuel as the continuous phase and an emulsified inorganic oxidizer salt solution or melt as the discontinuous phase . these oxidizer and fuel phases react with one another upon initiation by a blasting cap and / or a booster to produce an effective detonation . the explosives contain a polypropene or polybutene derivatized water - in - oil emulsifier and a density reducing agent in the form of expanded organic microspheres having a nonpolar surface and comprising homo -, co - or terpolymers of vinyl monomers . this combination of polypropene or polybutene derivatized emulsifier and organic microspheres has been found to be particularly advantageous in the water - in - oil emulsion explosives of the present invention .