The aim of this paper is to find out whether the cost shocks occur in the passenger rail transport, whether it can cause problems of financing as well as to evaluate the ways which are used by the purchaser of public transport to change the subsidy for carriers in case of cost shock. Results have shown that costs shocks can negatively impact financing of the subsidised passenger railway transport, so purchasers of the transport services must be extremely cautious in setting the tender documentation. So that purchasers avoid time-inconsistency solution, it is necessary to set the change in the subsidy in the contract. None of the tested clauses used by purchasers is ideal. We can see over-/under-compensation. The clause with 55 % of the consumer price index and 35 % of the change in labour costs in the transport sector reaches better results especially in contracts with vehicles purchased by the carrier.