Are you solo or in a group? What server and time do you play? If solo, Oil can be decent, as can salvage. Keep in mind, oil is a lot heavier than most items, so you really don't earn much.
If you are in a group, get some gear and run diamonds. However, I don't recommend running diamonds during prime time as big gangs will rob you. If you have a lot of money, farming anything in a HEMITT/Tempest can be profitable, but be careful, they are slow and huge targets.