Barium is present in one of the additives used in jet fuels and jet turbine oils. Its purpose is to increase the oil /fuel conductivity and avoid accumulation of electrostatic charges in the fluid which could generate fire (typically we target 400 pS as a minimum conductivity to lower fire risks).
Search for STADIS 450 from ExxonMobil, homologated officially for such purpose.
It's probably a di-nonyl-Naphtalen barium sulfonate.