At least in Switzerland for example a lot of the Miniprix, BP[1] and Shell gas stations have all the same gas as it comes via the same supplier which is Oel-Pool AG and its subsidiaries. Oel Pool is also selling their surplus gas via their own low cost gas station networks which has the symbol of an elephant trunk.
[1] https://www.oel-pool.com/info-center/neuigkeiten/detail/uebe...