In an illiquid (commodity) futures market, several days may pass between trades in a contract. If the traders' positions must be marked to market every day, a price must be quoted even on days without trades. Question: Is there a commonly accepted rule for how the price is set on days without trades? Or does the practice differ materially across contracts and/or exchanges?
(I am not asking for a list of possible methods but rather methods actually in use and their popularity. E.g. I am familiar with an exchange where the price is set by a person without following any written rule. I wonder how common this is, and if it is not, then what the common practice is.)