Crude Oil does not exist as item, but can be collected the same way as water or lava by using an empty bucket: hold an empty bucket and right click on an oil source block to fill the bucket with oil. Liquid pumps from compatible mods may work too.
Since the version 184.108.40.2060, Portable Oil Extractor is no longer essential to collect Crude Oil, although players still have this option.
Oil generates between y-levels 15 and 34 in small underground reservoirs mostly in low altitude and flat biomes. It is more common in desert and ocean biomes.
Oil generation can be disabled in the config. However, it will not be possible to produce fuel if there is not any other mod that adds oil.
Crude Oil will spread on up to 2 blocks from the source block on a solid surface, shorter than lava outside the Nether. Like water, spreading crude oil will wash out plants and, against logic, extinguish fire. It has no current. Players immerse in it will have a pitch black sight and barely can see anything, unless in 3rd-person camera.
On the other hand, it lacks the other fluid-like properties: players and mobs cannot swim in it, it is not possible to drown and thus get any damage, and it does not affect mining speed. (as of Galacticraft 4, Crude Oil has been updated and works exactly like water.) Crude oil will not explode in contact with fire, as fuel blocks do.
Oil from other mods can be used in the refinery, using the same means.
Crude Oil has the ID name