@wikipedia

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

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

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

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

	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	< 0.5 *	> 70°
Condensate	0.69 ÷ 0.816	45° ÷ 70°
Light Oil	0.816 ÷ 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.