completed machine would almost certainly be less than half that of a completed machine of the same kind. How s1(3) operates has been the subject of a detailed and critical analysis by Robert Goff J in the case of BP Exploration Co Ltd v Hunt (No 2), the defendant was granted a concession to explore for oil in Libya. He did not have the physical resources to carry out the exploration himself, so he sold a half share in the concession to BP, on condition that they would bear the initial cost of exploration. Accordingly, under this arrangement, BP’s expenses at the outset were likely to be very substantial, but on the assumption that oil was discovered, that expenditure would be recouped as oil continued to come on stream. The nature of the contract was that should oil not be discovered, the risk would be borne by BP, but, on the assumption that oil was discovered, BP’s expenses would be paid for out of the defendant’s receipts. Oil was discovered in 1967, but in 1971, the Libyan Government expropriated BP’s share of the concession and, in 1973, the defendant’s share was also expropriated. Accordingly, BP had received some payment, but this went only so far as to cover two-thirds of their initial expenditure. On the other hand, since the defendant had no expenses, all moneys received by him amounted to profit once the concession had been paid for. Goff J adopted a two stage approach to s1(3), stating that it was necessary first to identify and value what benefit had been conferred on the defendant, since on the wording of s1(3), this set a ceiling on the amount which could be awarded by way of a just sum. Secondly, it was necessary to award a just sum, taking account of the value of the benefit conferred and the cost to the performer of the work he had done prior to the frustrating event. For these purposes, the benefit to the defendant will be assessed by reference to the end product of the service provided by the other party: BP Exploration Co Ltd v Hunt (No 2) [1979] 1 WLR 783, p 799