Petroleum geologists and engineers are using subsurface mapping successfully. Structural analysis evaluates craton style, unconformities, folding, multiple lithologies, facies changes and fault displacements Large fields are found in structural traps, whereas smaller and more numerous fields are found in stratigraphic traps, Seismic method measures elastic longitudinal and transverse elastic wave energy. Targeted infill drilling reduces development costs by almost 50% vs. blanket drilling plus adds more oil recovery in select field sections Sidewall coring determines which zones should be production tested.The interpretation process determines which evaluation tools are used based on project economics and facies packages, Rock typing measures lithology properties, porosity vs. permeability, resistivity vs. water saturation, apparent density, capillary-pressure curves, and residual hydrocarbon saturation vs. initial hydrocarbon saturation. Clastic percentage and ratios determine where the best reservoir potential is located in basins by categorizing pinching or thickening pay zones and indicating seal direction