In one of their early works,
Miranda and Persson have classified all possible configurations of singular fibers for
semistable extremal elliptic fibrations on K3 surfaces. They also obtained the
Mordell-Weil groups in terms of the singular fibers except for 17 cases where the
determination and the uniqueness of the groups were not settled. In this paper, we
settle these problems completely. We also show that for all cases with ‘larger’
Mordell-Weil groups, this group, together with the singular fibre type, determines
uniquely the fibration structure of the K3 surface (up to based fibre-space
isomorphisms).