Les is currently an Adjunct Professor in the Basin and Petroleum System Modeling, a Stanford University Industrial affiliate program that he was one of the three co-originators in 2005. He graduated from the University of Oregon, Eugene, OR with a B.S. in biology in 1964 and a M.S. in Geology in 1966. He worked 8 years for Shell Oil Company in Exploration where he was the lead investigator in the Ventura-Santa Barbara Basin source rock and migration study, the first investigation of its type in exploration for this company. Les worked 30 years for the U.S. Geological Survey where he carried out resource assessment studies in Alaska, Colombia, Venezuela, and Canada. The Alaska studies included the Cook Inlet and North Slope. Since 1981, he has investigated and popularized the petroleum system through talks, courses, and AAPG Memoir 60, The Petroleum System—From Source to Trap, for which he and his co-editor received the R. H. Dott, Sr. Award in 1996. Published in 1994, this popular book was reprinted twice and sold out all 4,000 copies and is now only available in CD. In 2017, he received AAPG Honorary Member Award and in 2021 the AAPG Sidney Powers Memorial Award, the society's third highest and highest award, respectively.