Thomas Ableman is the new marketing director for the train operating company but the pitch process is thought to have been started several weeks ago.
Procurement and head of marketing and PR Kirsteen Robertson have been working on the tender.
Incumbent McCannn Erickson is believed to have repitched and the shortlist is thought to have been drawn up.
Chiltern Railways is owned by Deutsche Bahn AG and is part of DB Regio, Deutsche Bahn’s local and regional service provider.
In March this year it handed its £13 million outdoor advertising contract to Titan Outdoor after a pitch against incumbent CBS Outdoor.
The train operating company won the tender for its franchise in 1996 and runs scheduled passenger services along the M40 corridor between London Marylebone and Birmingham Snow Hill and London Marylebone to Aylesbury via Amersham along the London Underground Metropolitan line.
In 2004 it took over services between Stratford-upon-Avon and London.