1. Regulators can set price controls to force monopolists to charge a price below profit maximising price, using the RPI-X formula
2. RPI-X+K formula where K represents the level of investment, used in the water industry and has allowed investment of £130bn
3. Gives an incentive for firms to be as efficient as possible as if they can lower costs by more than X they will enjoy increased profit
4. Prevents excessive prices and ensures that gains are passed onto the consumer
5. Problem is that it is difficult to know where to set X due to rapid improvement in technology and because any information on what the efficiency gains will be have to come from the firm, who could easily lie as there is asymmetric information
6. Maximum prices could be set where the price is equal to the MSC, ensuring monopolies are allocative efficient but it is difficult for governments to know where they should set the price as they do not know the exact allocative efficient output and it can also increase dynamic inefficiency as firms are unable to maximise profit so may not invest