the abscissae values represent elapsed pumping time the curve portion 10 having a constant positive slope is indicative of 34 pkn 34 behavior of a fracture where it extends outwardly into the rock with vertical height confinement the curve portion 11 which has a substantially flat slope indicates opening of natural fissures in the rock and accelerated leakoff of fracturing fluid or stable height growth into a barrier curve portion 12 which has a positive slope of about one 1 is indicative of the onset of a 34 screenout 34 where bridging of a fracture by proppants will restrict further fracture extension curve 13 having a constant negative slope shows 34 kgd 34 type of behavior of a fracture where the height is greater than the penetration distance of the fracture into the formation or a radial penny shaped fracture the plots shown in fig1 are the so called 34 net pressure 34 plots and are well known in the art as a diagnostic tool for interpretation of fracturing pressure data the pressure data can be measured during the fracturing operation in any suitable manner for example by use of a downhole pressure gauge or a dead string for measuring surface pressures that are representative of downhole conditions the pressures also can be inferred from surface measurements of injection pressures taking into account the friction losses in the pipe and the hydrostatic head pressure thus the term 34 measuring 34 as used herein and in the claims is intended to encompass any procedure whereby the pressure data is obtained the basic.