This article discusses the principal claims made for the Resource Rent Tax (RRT) by Garnaut and Clunies‐Ross (1975, 1979) relating to its efficiency and potential for generating tax revenue relative to other forms of resource taxation, and also their concern about the greater uncertainty of these revenues. An analysis of the risk‐return trade‐off associated with a shift from ad valorem royalties to an RRT finds this shift to be worthwhile. Estimates are also provided of the foregone tax revenue from the North West Shelf associated with the use of ad valorem royalties rather than the RRT.