After he was honorably discharged in 1946, O'Neill studied physics and mathematics at Swarthmore College. As a child he had discussed the possibilities of humans in space with his parents, and in college he enjoyed working on rocket equations. However, he did not see space science as an option for a career path in physics, choosing instead to pursue high-energy physics. He graduated with Phi Beta Kappa honors in 1950. O'Neill pursued graduate studies at Cornell University with the help of an Atomic Energy Commission fellowship, and was awarded a Ph.D. in physics in 1954.