We prove that a general n-fold quadric bundle Q n−1 → P 1 , over a number field, with anti-canonical divisor of positive volume and discriminant of odd degree δ Q n−1 is unirational. Furthermore, the same holds for quadric bundles over an arbitrary infinite field provided that Q n−1 has a point, is otherwise general and n ≤ 5. We also give similar results for quadric bundles over higher dimensional projective spaces defined over an arbitrary field. For instance, we prove the unirationality of a general n-fold quadric bundle Q h → P n−h with discriminant of odd degree δ Q h ≤ 3h + 4, and of any smooth 4-fold quadric bundle Q 2 → P 2 , over an algebraically closed field, with δ Q 2 ≤ 12.