Figure 2. Map of pressure-depth (p-d) gradient values for upper Morrowan reservoirs in the Anadarko basin and Oklahoma portion of the Hugoton embayment. P-d gradient values range from extremely overpressured (>0.9 psi/ft) in the deep basin to abnormally underpressured in the Oklahoma Panhandle (<0.3 psi/ft). This intrastratal change in pressure is convincing evidence of regional pressure seals. The location of the potentiometric surface cross section (Figure 3) is shown.