Taking Stock: What Do All These Large Numbers Mean?

When the debate on drilling in the Alaska National Wildlife Reserve (ANWR) picked up around the year 2000, I was informed by a Texan that there were 900 billion gallons of oil in the ANWR. (Turns out that is the estimated amount of oil-in-place, not the ultimate recovery, which is far less.) Since such numbers are normally expressed in barrels, I wondered who had published this number and what their agenda was? It occurred to me that any reasonable fact could be obscured by picking units of measure which virtually no one can grasp. Example: The length of a football field is (exactly) 914.4 Giga-Ångstroms. That's 914 Billion Ångstroms. The calculations:

100 yards x 36 inches/yard x 2.54 cm/inch x 1,000,000 microns/m x 10,000 Ångstroms/micron / 100 cm/meter = 914,400,000,000 Ångstroms
(According to myth, the yard was defined to be the distance between Henry I's nose and his thumb.)

One credible estimate of the ultimate amount of conventional (pumpable) oil on the earth is 1,750 Gb (billion barrels). What does that mean?

Please explain the significance of two trillion barrels of oil.

1,750 Gb, the estimate of all the conventional oil that there ever was or ever will be, is less than the amount of sunlight that intersects the earth in one 24 hour day. (This is not to say that all of the solar energy that intersects the earth hits the earth’s surface. The earth’s atmosphere absorbs and reflects a large portion of that solar energy. The point is to provide readers with a sense of the scale of the solar resource.)

1,750 G-barrels x 5,800,000 BTU/barrel = 10.15 x 1018 BTU, which is less than ...
445 BTU/ft²/hr x 24 hrs x 49,240,000 mi² x 5,280² ft²/mi² = 14.7 x 1018 BTU

In the short term view of one year, the total global annual consumption of energy (400 quads) is roughly equivalent to 40 minutes of sunlight:

400 x 1015 BTU = 445 BTU/ft²/hr x 0.67 hrs x 49,240,000 mi² x 5,280² ft²/mi² = 407 x 1015 BTU

Some people say that "solar" is a diffuse, insignificant source of energy. How long would humanity survive if we had only oil to heat the earth?!

[Note: 49 million mi² is the area of the earth -- at 7,918 miles diameter -- intersecting the sun's light.]

Global Solar Energy Balance1  Amount in Terawatts
 Solar Energy Input


 Reflected to Space Immediately


 Absorbed and Then Reflected as Heat


 Used to Evaporate Water (Weather)


 Captured by Plant Photosynthesis
(Net Primary Productivity)



 Total Energy Used by Human Society


 Total Energy Used by US Society


 Total Human Food Energy


Cited by Ecology 10 Tutorial, Lecture 4: Physical Background: Energy, Frank Orme, Instructor

See also:

1,750 Gb of oil is equal to 67 cubic miles. The (conventional) oil already consumed globally, plus all the oil yet to be consumed, could be fit into a cube slightly over 4 miles on a side!

1,750 G-barrels x 42 gal/barrel / (7.48 gal/ft³ x 5,280³ ft³/mi³) = 66.8 mi³ = (4.06 mi)³

One cubic mile = 26.2 billion barrels
one cubic kilometer = 6.28 billion barrels

If spread over the entire surface of the earth -- land and oceans combined -- 1,750 Gb of oil would constitute a layer 21.5 mils thick -- about the equivalent of a spark-plug gap!

67 mi³ / 197,000,000 mi² x 5,280 ft/mi x 12 in/ft = 0.0215 in = 21.5 mils

On the other hand, the USA population consumes its entire weight in oil every week!

17,000,000 barrels/day x 42 gal/barrel x 7.5 lbs/gal x 7 days/week / 250,000,000 persons = 150 lbs/week/person

revised 2004 December 8
revised 2004 September 6
previously revised 2000 August 7