Totally depends on the skills that a person has as to the arrangements that he can broker with the oil company. I spent most of my life holding two or more jobs. Bear in mind that each place that you work at will at times, demand that you attend to their emergencies 1st. At that time, you have to remind them of your working agreement with them. Don't take a part time job without informing them of your commitment to your primary job. Remember one time that I was working evening shift at the refinery and hauling asphalt on my days off. Got a call from the trucking co one evening and they needed a load hauled the next morning. I told them that I would have to be back in town by 1 PM in order to go to my regular job. They assured me that it would be no problem, haul the load 150 miles, unload into their working tank and return home. When I got there, the road foreman told me that they would shoot off of my truck that day and they wouldn't be finished until around 4PM. I asked him to use their work tank and he refused. I got back in my truck, returned to Big Spring and got fired for not staying on the job site. A week later they were calling me again wanting me to go back to work. Paid pretty good so I did a lot more hauling for them but it was always on my terms.