oil drilling rigs (or at least the fields they drill) were nerfed somewhere along the line. They require MV power at least now (even for the lowest tier oil rig - the higher tiers drill several chunks at once, but with the same effective speed), and last I checked, there was only about a 26% of getting an oil or raw oil field that could even produce enough to break even (presuming you process the oil into light fuel and use it to power the oil rig). 22% with light oil. If you want to get double the energy you used for drilling, that's 14% with oil (maybe called "crude oil" now, not sure) or raw oil, and 10% with light oil.
There is a still-open bug about it here: https://github.com/Blood-Asp/GT5-Unofficial/issues/1238