Oscar E. Monnig died on May 4, 1999 in Fort Worth, Texas, where he had lived since his birth in 1902. In 1925, he earned a law degree from the University of Texas, where his "only formal scientific training", as he put it, was signing up for an astronomy course that was promptly cancelled for lack of enrollment. He worked for, and eventually headed, the dry goods business his family owned in Fort Worth until the sale of his company in the early 1980s. Although his vocation was business, his avocation was always meteoritics and astronomy. As a young man, he founded the Texas Observers astronomy club to promote interest in meteorites. To satisfy his curiosity about "rocks from space," he traveled to the Field Museum, American Museum, and Smithsonian Institution to view and discuss meteorites. The trip left him somewhat discouraged, when the curators at these museums treated him "as a nobody" and did not even offer to show him a meteorite.

The early experience further fired Oscar's lifelong passion for meteorites and his drive to gather his own collection. He began collecting meteorites in the early 1930s, amassing one of the most significant private collections of his day. Oscar traveled widely on family business and established a network of business associates, employees, customers, and perhaps most importantly, local newspaper editors. It was this network that would ultimately lead Oscar to many of his new recoveries. His main competition in meteorite collecting was Harvey Nininger, with whom he would often collaborate when they would both arrive at a locality simultaneously. Oscar retained voluminous correspondence providing not only an invaluable history of the collection, but also a glimpse into the early times of meteoritics. Letters from barely literate "dustbowl" farmers state how Oscar's payment for a meteorite (at the standard rate of $1.00 per pound) was the largest check received on the farm that year.

With no formal scientific training and a business to run, Oscar was not a prolific publisher, although he did write significant papers on the Odessa meteorite crater and several of his meteorites. His Odessa crater paper has the distinction of being the first paper published in the "Contributions of the Society for Research on Meteorites," the precursor to the current "Meteoritics & Planetary Science." His mark was made in the meteorites he recovered, including such important specimens as the unusual carbonaceous chondrite Bells and the nickel-rich iron meteorite Tishomingo. In a series of transfers between 1977 and 1987, Oscar donated his collection of approximately 3,000 specimens from 400 different meteorites to Texas Christian University, fulfilling his lifelong wish to keep his collection in the city that had supported his family business. The Monnig meteorite collection is a lasting tribute to Oscar's long and successful career in meteoritics.

Oscar was also an important early influence in the Society for Research on Meteorites (later the Meteoritical Society). He was a Charter Member and Fellow of the Society, serving as both a councillor (1941 – 1950; 1958 – 1966) and secretary (1946 – 1950). After a 60 year membership, the Society has lost one of its great early pioneers.

— Arthur J. Ehlmann and Timothy J. McCoy