An interest in a well or property that becomes effective at a specified time in the future or on the occurrence of a specified future event. The right of future possession of an interest in a property when a specified condition has been met. Such as when Australian company Origin acquired its CSG assets from Tri-Star Petroleum in 2002, it gave Tri-Star the right to take back 45 per cent of its share in each field once it had achieved payback, which is judged on a formula linked to Origin’s capital and other costs, which mean Origin could be compelled to hand a significant proportion back to Tri-Star Petroleum.