Is there a problem with working for any oil company?

The basic principle is that all actions are permissible unless there is a religious text that prohibits them. If a person's work in these companies is not associated with something forbidden—such as transporting alcohol or pork—then their work is lawful. Otherwise, it would be unlawful due to the assistance it provides in sin, and Allah the Almighty says: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression).