@wikipedia

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

Very Small	Small	Medium	Big	Giant	Super-Giant
< 7 mln bbl	7 ÷ 70 mln bbl	70 ÷ 200 mln bbl	200 ÷ 700 mln bbl	700 ÷ 2,000 mln bbl	> 2,000 mln bbl
< 1 mln ton	1 ÷ 10 mln ton	10 ÷ 30 mln ton	30 ÷ 100 mln ton	100 ÷ 300 mln ton	> 300 mln ton

	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°

* – with reference to air.

	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
Low viscous oil	< 1
Medium viscous oil	1 ÷ 10
High viscous oil	10 ÷ 100
Extra high viscous oil	100 ÷ 10,000
Bitumen	> 10,000

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.

Very Poor	Poor	Medium	Good	Very Good
< 0.45	0.45 ÷ 1.0	1.0 ÷ 3.5	3.5 ÷ 8.0	> 8.0

Very Fast Water	Fast Water	Agile Water	Agile Oil	Fast Oil	Very Fast Oil
>5	1.5 ÷ 5	1.0 ÷ 1.5	0.5 ÷ 1.0	0.2 ÷ 0.5	<0.2

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

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