After graduating from law school in 1957, Oaks spent a year as a clerk to Chief Justice Earl Warren of the U.S. Supreme Court. After his clerkship, he practiced at the law firm of Kirkland & Ellis in Chicago, specializing in corporate litigation. Oaks had worked with this firm twice before, first during a summer in law school and then for a few months before he began his clerkship with Justice Warren. When Oaks began work at Kirkland & Ellis he worked under Robert Bork but he was quickly appointed as one of the principal lawyers. He mainly worked on cases for clients Standard Oil of Indiana, B. F. Goodrich and Chemetron Corporation, but also assisted with cases with several other companies. Initially they lived fairly far west in the suburbs of Chicago, but in 1960 the Oaks bought a house in Elmhurst, Illinois.