We argue five main propositions. Firstly, the choice between royalties and profit-based taxation involves an efficiency trade-off, between diminished incentives to produce output on one hand, and diminished incentives to minimize costs on the other (as in Laffont and Tirole 1993). So the Brown tax is indeed a tax, and one that reduces the incentive to mine. Next, the ex post Resource Super Profits Tax (RSPT) falls on quasi-rents as well as on rents, and therefore involves some expropriation. Third, there may be a case in favour of a retrospective RSPT or the like, but it has yet to be made persuasively. Fourth, the successor to the RSPT – the Minerals Resource Rent Tax (MRRT) – has many of the inefficiencies of the RSPT but adds some further serious inefficiencies of it is own. Last, the value of revenues from taxes such as the RSPT and the MRRT is usually over-stated, as those revenues are highly risky. The failure to take account of the risky character of those income streams amounts to fiscal illusion and makes it more likely that unwise spending commitments will be made.
