Cultivation: Hash-Oil can be (and is) produced from any kind of Hash, so the cultivation method varies with the origin country.
Production: Hash-Oil is very simple to make: the dried and powdered Buds are soaked in a (preferably Non-Polar) solvent for a couple of weeks, then the solvent is evaporated and what remains is Hash oil.
Color: Extremely dark green to nearly black.
Smell: Highly aromatic and spicy.
Taste: Highly aromatic and spicy, taste however varies considerably with the source material.
Consistency: Hash-Oil (even a highly pure one) is quite thick and hard at room temperature. At body temperature it becomes extremely sticky, when heated it becomes a liquid.
Effect: Very physical and stony high. Most stony and physical high you can find.
Potency: Potent to very potent.
Availability: Quite rare but becomes available from time to time, probably a lot is produced in someone's kitchen.
Various: Nearly always some form of Alcohol is used as solvent. While this works quite well (especially if the source material is already good) there is a lot of Chlorophyll and other inactive substances in the product.
A purer form of Hash-Oil, usually called Honey-Oil, is produced by extracting the material with Petroleum-Ether (or some other non-polar solvent) and separating the water soluble substances from the insolubles. Unfortunately in the origin country usually low quality Dope is used in the production of Oil.
It is also quite easy to be ripped off when buying oil since it's very easy to adulterate.