When most people think of Oxford, what comes to mind are images of bright minds debating quantum physics or the existence of God. But even the brainiest sometimes need a lesson in common sense.

That’s exactly what the bursar at St. John’s College—the most richly endowed college at Oxford—delivered when he responded to students occupying his 15th-century quadrangle and refusing to leave until the college divested its oil-company shares. The students want the college to sell the more than $10 million of its endowment now invested...