The airline currently uses Four for both its consumer and corporate PR.
Bmi head of comms Sam Day said: 'We're going through a whole reviewing process, now that we have been bought by Lufthansa. It's a case of responding to the way the business is changing.'
Day added that the fees were still 'up in the air'.
Day was appointed a year ago as the airline's first head of comms. She joined from the Gold Medal Travel Group, where she was PR manager.
Bmi is still inviting agencies to pitch and does not yet have a pitch list. The airline does not intend to put its corporate PR business out to pitch.
Lufthansa withdrew bmi from sale last November, to concentrate on trying to turn around the airline itself.
In February, low-cost subsidiary airline bmi baby hired Rabbit as its first retained digital PR agency. The newly launched sister agency to Cow PR manages all the airline's online comms.