Jack J. Grynberg (January 21, 1932 – October 11, 2021) was an American businessman. He was a Denver-based oil and gas developer who amassed a multibillion-dollar fortune in the oil and natural gas sector. As of 2019, he was in a long-running litigation to regain control of companies he founded from his ex-wife and three children, or failing that, around $400 million in back pay. Early life Born to a Jewish family in the Polish city of Brest (now Brest, Belarus), Grynberg was in the second grade when the Nazis invaded Poland. He stated that he joined the resistance and by the age of 12 he was fighting in the forests of Belarus, and fought until 1945. He then moved to Colorado, where he attended the Colorado School of Mines, married, and began raising his three children. He also claimed that he worked as a spy for the US Army in 1957 and 1958. He had a master's degree in Petroleum Engineering and Refining from the Colorado School of Mines. Career Early career Grynberg made his first million dollars by the age of 30 when he formed a company, Oceanic Exploration Co., that reworked a previously drilled gas well that had been abandoned by Amerada Hess Corporation as "noncommercial". After reviewing and interpreting data from the area, he concluded that Amerada Hess was wrong. His reworked well led to the discovery of the Nitchie Gulch gas field in Wyoming, leading Grynberg to become a millionaire in 1962. From there he engaged in several successful domestic and international oil and gas exploration programs, and took the Oceanic Exploration public in 1972. Later career Grynberg was also instrumental in the 1990s in helping discover the Kashagan Field in Kazakhstan, one of the largest oil field discoveries in the last 30 years. The Kashagan Field is estimated to hold of recoverable oil and of natural gas. Grynberg was one of the first western oilmen to develop relations with Kazakh President Nursultan Nazarbayev before the collapse of the Soviet Union. This relationship and others provided him with access to complex and confidential data. According to court records, it was Grynberg who provided the introductions and data for BG, BP, Statoil, ARCO, Transworld Oil and others to enter the region in the late 1980s and early 1990s. When the consortium of major American oil companies fell apart, BG cut its own deal for the Karachagnak