@wikipedia

Hydrocarbon Reserves Classification provides the primary insight into the size, uncertainty and structure of the Hydrocarbon Reserves.

By recoverable volume

Super-Giant	Giant	Big	Medium	Small
> 5 billion bbl	> 500 million bbl	> 50 million bbl	> 5 million bbl	< 5 million bbl

By reserves uncertainty (SPE)

2P = Proven P90 + Probable P50
1P = Proven P90		Probable P50	Possible P10
Proven developed (PD)	Proven Undeveloped (PUD)

By petroleum density at surface

	Gas	Condensate	Light oil	Medium Oil	Heavy Oil	Extra Heavy Oil (Bitumen)
kg/m³	< 702	702 ÷ 801	801 ÷ 870	870 ÷ 920	920 ÷ 1000	> 1000
API	> 70°	45° ÷ 70°	45° ÷ 31.1°	22.3° ÷ 31.1°	10° ÷ 22.3°	4° ÷ 10°

By petroleum mobility [old]

	Specific Gravity *	API Gravity	High perm	Medium perm	Low perm	Tight (Shale)
	frac	API	> 100 md	10 md ÷ 100 md	0.1 md ÷ 10 md	< 0.1 md
Gas	< 0.702 *	> 70°
Condensate	0.702 ÷ 0.802	45° ÷ 70°
Light Oil	0.802 ÷ 0.87	31.1° ÷ 45°
Medium Oil	0.87 ÷ 0.93	20.7° ÷ 31.1°
Heavy Oil	0.93 ÷ 1.0	10° ÷ 20.7°
Extra Heavy Oil (Bitumen)	1.0 ÷ 1.04	4° ÷ 10°

* – with reference to air.

where box colours mean:

Conventional Reserves

Unconventional Reserves

Unrecoverable Reserves

and the ranges of properties in the table are only tentatively define the category based on the industry statistics and conventions, which vary over history and locations.

By petroleum mobility

	Dynamic fluid viscosity	High perm	Medium perm	Low perm	Tight (Shale)
	cP	> 100 md	10 md ÷ 100 md	0.1 md ÷ 10 md	< 0.1 md
Condensate
Light Oil
Medium Oil
Heavy Oil
Extra Heavy Oil (Bitumen)

where box colours mean:

Conventional Reserves

Unconventional Reserves

Unrecoverable Reserves

and the ranges of properties in the table are only tentatively define the category based on the industry statistics and conventions, which vary over history and locations.

By sulfur content

Sweet crude	Sour crude
Sulfur < 0.5%	Sulfur > 0.5%

By reservoir gas conditions

Undersaturated Oil Reservoir		Saturated Oil Reservoir		Natural Gas Reservoir
Black Oil Reservoir	Volatile Oil Reservoir	Gas Cap Oil Reservoir	Oil Rim Reservoir	Retrograde Gas Condensate Reservoir	Wet Gas Reservoir	Dry Gas Reservoir
		both underlying Natural Gas Reservoir