A Saudi Aramco oil tank. : Saudi Aramco’s public market debut, which would have been the biggest ever, is being postponed. Instead, the Middle Eastern oil giant is focused on buying a stake in Sabic, a huge publicly traded chemical maker controlled by the kingdom’s sovereign wealth fund. Why pause? Arranging such a huge I.P.O. is complex, and oil prices have rebounded, which made the offering less attractive. But the decision hurts several groups: • The Saudi government misses out on a multibillion-dollar windfall that it said would finance a transformation of its economy. Aramco officials insisted that the I.P.O.