A subterranean formation having natural fractures, which is to be subjected to hydraulic fracturing, is first pre-treated with an ultra lightweight (ULW) proppant having an average particle size between from about 12/20 to about 40/70. The small ULW proppant flows into the natural fractures and packs the fractures. The formation is then subjected to hydraulic fracturing. The pre-treatment serves to enhance the effective propped fracture length of the formation during the hydraulic fracturing by reducing the loss of fluid from the subsequently pumped fracturing fluid. The method is applicable to hydrocarbon bearing formations as well as non-hydrocarbon bearing formations and has particular applicability to coal beds.