What is the ruling on the work of a petroleum engineer, and is he considered a participant in sin if oil revenues are unjustly stolen in his country?

It is a legal principle that the default status of all things—such as work and jobs—is permissibility and lawfulness. Nothing deviates from this original status except with evidence that necessitates prohibition and unlawfulness. This is a manifestation of Allah's mercy and the ease of the Sharia. What has been mentioned about the work in question does not necessitate its prohibition, so the work remains on its original status of permissibility.