What is the ruling on receiving a monthly salary for delivering sermons (khutbah) and leading prayers (imamah) in a mosque affiliated with an oil company, and does that diminish the reward if it is permissible?

There is no harm in taking a wage for leading prayers (Imamah) and delivering sermons (Khutbah), as long as it is with the knowledge and approval of the company's management, due to the generality of the Prophet's (peace be upon him) saying: "Indeed, the most deserving of what you take a wage for is the Book of Allah." With a note that taking a salary diminishes the reward and recompense.