Fuel price caps are one of the potential regulatory tools for controlling wholesale electricity prices when fuel prices are volatile. In this paper, we introduce a theoretical model to study the effects of such caps on firms’ bidding behavior and clearing prices in spot market auctions. We then use data from the Australian National Electricity Market (NEM), which recently implemented such caps, to empirically test and compare their effectiveness in three different states. Our theoretical findings suggest that fuel price caps can be binding, especially when electricity demand is lower and competition among generators is higher. When demand is high, alternative policy tools, such as market price caps, may be more effective in controlling auction prices. Our empirical analysis employs various techniques, such as Generalized Additive Models (GAM) and machine learning algorithms, to test the effectiveness of price caps in the NEM. We find mixed results regarding the effectiveness of fuel price caps in different states. Specifically, fuel price caps reduced wholesale electricity prices in Queensland and New South Wales, while they were not effective in controlling wholesale prices in Victoria.