Total Liquids

There are a fair number of reports which present a particular data series:

Total Liquids in Barrels over Time.

For an example of this I will use a recent post to The Oil Drum which features a chart based on US DOE EIA data for total liquids in barrels over time.

January Oil Supply
Stuart Staniford / The Oil Drum / February 24, 2012

Total liquid fuels were at all time highs in January,
according to OPEC and the IEA.

So what is wrong with this chart?

Energy Units and Conversions (link)
by Dennis Silverman / U. C. Irvine, Physics and Astronomy

Crude Oil [contains] 5.6 million BTU/barrel

Natural gas liquids [contains] 4.2 million BTU/barrel

Approximate values, but good enough for this statement:

To combine various liquid fuels with different energy densities into a single count of barrels over time conceals reductions over time in the available energy from those liquid fuels.

As an analogy, would you expect to see a report covering up a copper shortage by showing only combined data of pounds of copper plus pounds of cement in an unspecified ratio? Yet few people question reports showing combined barrels of liquids that contain very different amounts of energy.

Creating a chart showing Total Liquids in BTUs (not Barrels) over Time would not be a complicated thing to do. Such charts probably exist in private and they probably look frightening because the world is probably running on less energy from liquid fuels over time now.