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On February 18 a cadre of political and energy heavyweights gathered in a teleconference with reporters to map out a new direction for U.S. energy policy.  Energy Secretary Stephen Chu, Interior Secretary Ken Salazar, Senate Majority Leader Harry Reid, and energy entrepreneur T. Boone Pickens discussed strategies to develop clean energy sources that will reduce U.S. oil imports.  The teleconference was a prelude to a conference on February 23 of the National Clean Energy Project that featured former president Bill Clinton and former vice president Al Gore (1).

A key element discussed during the teleconference was a plan to power the long-haul trucking industry with natural gas instead of diesel fuel.  The plan would reduce air pollution and oil imports, a plan that Boone Pickens has been promoting since 2007.

“We need to work hard to use more domestic energy in our transportation and rely less on foreign oil.  Natural gas is the only way to make a difference now,” Pickens said.  “We are absolutely overwhelmed with natural gas…it’s so abundant…the United States has plenty of natural gas onshore in shale basins,” he said.

Secretary Salazar agreed, saying, “There are natural gas resources being developed all over the country.”  However, he added that increased demand for natural gas to power vehicles will not lead to expanded leasing of the Outer Continental Shelf.

Senator Reid and Mr. Pickens focused on the trucking industry as a likely first stage for conversion to natural gas.  “We want to start by fueling almost 400,000 18-wheelers immediately.  This would cut imports significantly,” the senator said (1).

CNG or LNG for Trucks?

We can test this red-hot plan to fuel the trucking industry with natural gas, by combining real-world numbers with cool-headed analysis.

The first item we need to settle is, what form will the gas be in at fueling stations and on-board?  We have two choices: compressed natural gas (CNG) or liquefied natural gas (LNG).  I will argue that LNG is the better choice based on the critical feature of energy density, measured in BTUs per unit volume.  CNG has only 25% of the energy density of diesel fuel, while LNG’s density is 58-60% (2).  It means that a given volume of LNG will power a truck almost 2.5 times farther than the same volume of CNG.

Personal observations apply here.  The organization I work for has a fleet of CNG vehicles: several small cars and a few pickup trucks.  CNG pickups are assigned to field personnel who travel to construction sites throughout the region, typically driving 100 miles a day.  Almost every day they must drive 3 miles from our yard to a special CNG fueling station and wait in line to gas up.  The high-pressure fuel tank, protected by a hard, plastic shield, occupies almost one-fourth of the cargo bin.

Employees who drive the small CNG cars have learned from unpleasant experience not to venture onto a freeway with less than a half tank of gas.  The gauge can plunge to “E” with alarming swiftness.  Stranded employees have no recourse but to call our garage for help.  The garage cannot simply send out a pickup with a gallon of gasoline, for they are not equipped to dispense CNG.  They must send a wrecker to tow the car to the fueling station.  So it goes with CNG vehicles.

Long-haul truckers, whose livelihood depends on continual travel pulling full loads, do not want to worry about making it to the next fueling station; few wreckers can tow a fully-loaded 18-wheeler.  Nor do truckers want to surrender 25% of precious cargo space to CNG tanks.

If our leaders are serious about displacing diesel fuel with natural gas, LNG is the logical direction for future long-haul trucking.  But LNG has its caveats.  The existing LNG fueling stations scattered around the country require highly-specialized, energy-intensive refrigeration and compression equipment to chill the gas to -260o F and compress it to high pressure to liquefy it.  But extensive expansion of LNG stations may not be economically feasible considering that the special equipment might cost $1 million a pop(2).  Most refueling stations take LNG deliveries by tanker truck.  Truckers, in turn, need insulated, high-pressure tanks on their rigs to maintain the temperature and pressure of LNG.  Rigs need roughly twice the tank volume to store LNG vs. diesel for the same driving range.

How Much Would LNG Reduce Oil Imports?

Assuming that the added costs are covered to produce and store roadside LNG, and that truckers take to the road with LNG-fueled rigs, how much will the conversion reduce oil imports, and how much would demand increase for natural gas?  Putting Sen. Reid’s “400,000 18-wheelers” to the test, we can estimate how much gas the trucks would consume and how much diesel fuel would be saved.

Trucks, their loads, and distances traveled, vary in size and mileage, but let us say that a typical 18-wheeler is driven 60,000 miles/year at 6 mi/gal of diesel.  Our typical truck, then, burns about 10,000 gallons a year.  Scaling up to 400,000 trucks, diesel consumption is ~4 billion gal/yr.  Expressing this in bbl/day, we divide by 42 gal/bbl and 365 d/yr; we come up with a diesel saving of 260,000 b/d.

The U.S. now imports roughly 13 million b/d in crude oil and products.  Thus converting 400,000 18-wheelers to LNG would reduce oil imports by roughly 2 %.

Now let us see how much demand for natural gas would increase.  To compare diesel to gas, we need to express both fuels in BTU.

–One gallon of diesel supplies ~138,000 BTU.  Doing the math, our truck consumes roughly 1.4 billion BTU/year.

–One cubic foot of natural gas supplies ~1,000 BTU.  Annual diesel energy expressed as natural gas, then, is 1.4 million cubic feet per truck.

–Scaling up to 400,000 trucks, annual gas consumption would be 560 billion cf.

–The last few years, the U.S. gas consumption was roughly 22 trillion cf/yr.  The increased consumption to fuel 400,000 trucks, then amounts to about 2.5%/yr.

We should note that this gas consumption only powers the truck fleet.  Cryogenic chilling and compression to produce LNG is not included, but could increase gas demand by 10%.

Is the Gas Plan Realistic?

The U.S. may be capable of fueling a major portion of long-haul trucks by increasing domestic gas consumption by 2.5 %, but we would only reduce oil imports by 2 %.  In order to achieve that small increment, downstream energy providers would have to overhaul fuel distribution at great cost by producing and trucking LNG all over the U.S.  Then there is the expense to replace the fleet of 400,000 trucks to burn LNG.

The lesson learned here is that significant changes in processes by which energy is supplied and consumed require massive influxes of capital across multiple industrial sectors at considerable financial risk.  Energy developments evolve slowly over decades, not in years.  Senator Reid’s plan cannot be accomplished in 10 years, much less “immediately” as he said.

Tom Standing is an engineer with 44 years of experience in the energy sector in both chemical and civil disciplines. He continues to use his background to assess the many developments taking place throughout the energy sector.  He has contributed many Commentaries to Peak Oil Review.


1. “Clean Energy Strategy Must Include NGV Component, Reid and Pickens Say,” Oil and Gas Journal, February 18, 2009

2. “Natural Gas Vehicles Gain in Global Markets,” Ibid, February 16, 2009