Abstract: This patent deals with methods to selectively excite and analyze the resonance phenomena existing in an enclosed oil, gas and or water reservoir, thereby locating its presence, by doing qualitative and quantitative estimates of its extent via forward modeling. The oil, gas or water reservoir is represented as a fluid filled crack system or as a fluid saturated sponge located in solid rock. This patent covers the actively excited response and details methods to optimize the excitation. Due to interaction between either fluid filled fractures or fluid saturated rock lenses and the surrounding rock, the incident seismic energy is amplified in specific frequency ranges corresponding to the resonance frequencies of such systems. Measurements are made over the survey area, singly or in arrays. These are first used to determine qualitatively the resonance behavior, by relating them to resonance signal sources and possibly their direction. Overall statistical analysis assesses dominant frequencies in the spectrum.