Summary Estimates of formation pore pressure before and while drilling are important inputs for well planning and operational decision making. A method is proposed to determine pore pressure from a combination of downhole drilling-mechanics parameters and in-situ rock data with the concept of mechanical specific energy (MSE) and drilling efficiency (DE). This pore-pressure estimation method (termed DEMSE) is based on the theory that energy spent at the bit to remove a volume of rock is a function of in-situ rock strength and the differential pressure that the rock is subjected to during drilling. A work flow is provided that illustrates the steps required to estimate pore pressure from drilling parameters and rock-mechanics data by use of the DEMSE method. Pore pressure estimated from the DEMSE method is compared with pore-pressure estimates derived through a conventional sonic log that is based on empirical technique for a deepwater well in the Gulf of Mexico (GOM). Pore-pressure estimates from the DEMSE method generally agree in magnitude and trend with the pore-pressure estimates derived from sonic-log data. The results of the DEMSE method have also been compared with pore-pressure estimates from the classical d-exponent (dXc) approach to highlight the advantages of DEMSE over traditional dXc methods. Finally, the importance of using downhole vs. surface data for pore-pressure estimation purposes, specifically torque measurements at the bit, is illustrated through a field example. These findings suggest that downhole drilling-mechanics data, when properly used, can provide reliable independent estimates of pore pressure in real time at the bit and can be used for post-well-analysis to assist with constructing pore-pressure forecasts.