In an automatic trade system wherein bids and offers in instruments as well as in combinations of instruments are received and a trade in an instrument or in a combination of instruments is performed when, for a certain number of that instrument or combination of instruments, a bid price matches an ask price, a method for generating estimated prices of instruments for a trade in a combination of instruments, comprises the steps of (i) identifying for each bid/offer in each one of said instruments its bid/ask price; (ii) storing the identified bid/ask price of the last bid/offer in each one of said instruments; and (iii) generating said estimated prices based on the stored bid/ask price of the last bid/offer in at least one of said instruments, which is comprised in said combination of instruments, independent on whether said last bid/offer still exists or not at the time of generating said estimated prices.