A gas pipeline loses pressure as the flow rate increases.  In fact, the flow is trans-sonic.  That means that to push gas through a long pipe, one has to start with a high pressure to get meaningful gas out the other end.  The longer the pipe for a given flow rate, the higher the pressure and the thicker the steel.

To keep wall thickness within economic bounds, land pipelines use booster pumps along the line to make up the pressure drop and keep the gas flowing.  Often a pipeline will be constructed and then uprated later with the addition of more booster pumping stations.

A 2,000 mile long pipeline without booster pumps would require extraordinary amounts of steel or else flow little gas.  Alternately, building booster pumps 20,000 feet underwater (and maintaining them) is as of yet an unmet challenge.

I think people here at TOD will accuse me of being technically optimistic to a fault  (some would say a HUGE fault! :-), but I have to say, that yes, a Transatlantic pipeline is out of the debate.  Stringing a cable from a spool on the back of an ocean liner is small game compared to the construction and repeating the repressuring of the pipeline at regular interval....it would require repeating stations with compressors and power sources sitting on the bottom of the deep oceans...technically, we're good, but we just ain't that damm good!  (don't we wish though...)

What is interesting however is the variety of ideas that are in play to move natural gas....here's one that has actually been explored by the Defense Department as far back as the 1950's....

Suppose you built larger than Hindenburg size airships.....and fill the supporting bladder with natural gas.....it is lighter than air by enough to be bouyant, since it is mostly hydrogen....Then you simply tow a couple of the balloons  with one powered airship.....with the weather satellites and good communication, you could steer above and around really rough weather (it would be at least as safe as a deep offshore oil rig in a hurricane!) and move the gas without liquification. :-)  

The balloons would have to be VERY LARGE to move enough to make it worth it,but if the airship is well designed aerodynamically, for examle, as a "delta
 type shape, they would be very stable.....

The Russians once had an even more radical approach....they were going to fill "floater" balloons with natural gas, and release them into the high altitude....then whenever winds carried them somewhere that had a market for gas, or close enough to it, the customer would send a plane up to capture and retrieve the balloons!  With GPS and electronic I.D., the customer would then be billed for the balloon!

And people call me an optimist!  :-)

Roger Conner  known to you as ThatsItImout