Mark W. Longman is an exploration geologist who specializes in the study of carbonate and sandstone reservoirs around the world. He has worked extensively with Paleozoic reservoirs in North America as well as Mesozoic reservoirs in the Rocky Mountain and Gulf Coast regions and Tertiary reservoirs in Southeast Asia,  the Mediterranean region, and the Uinta Basin of Utah. His emphasis is on defining the nature of oil and gas reservoirs from depositional and diagenetic textures as determined from cores, cuttings, thinsections, and wireline logs. He has special skills relating hydrocarbon production to features such as facies types, porosity development and distribution, and diagenetic fabrics. He has worked as an exploration geologist and a research geologist for major oil companies, and ran his own consulting business from 1984 to 2006 before joining Questar Market Resources.