def giip(area=40, res_height=20, porosity=0.25, avg_water_saturation=0.4, gas_vol_factor=0.00533):
    """Returns the estimate for gas initially in place (SCF) given the area (acres), reservoir height (ft),
    porosity (fraction), average water saturation (fraction), and the gas formation volume factor (RCF/SCF)."""
    return (43560*area*res_height*porosity*(1-avg_water_saturation))/gas_vol_factor