Provided is a method for providing a recommended operating condition with which an oil refinery device can be operated more efficiently. A server 20: acquires past operational data for a device, a scheduled operating condition which is an operation condition for the device scheduled by a user, and plant information including at least a usage expiry time of the device; creates a user-specific catalyst deterioration function from the past operational data; calculates, on the basis of the catalyst deterioration function, the plant information, and the schedule operating condition, a recommended operating condition that achieves a catalyst lifetime which is later than the usage expiry time of the device and is earlier than the catalyst lifetime when the device is operated under a scheduled operating condition calculated on the basis of the scheduled operating condition and the catalyst deterioration function; and transmits the recommended operating condition to a user terminal.