1.   Gas will become, along with hydro-electricity, the largest single energy source.

2.   Liquefaction of Gases A gas becomes more difficult to liquefy the higher its temperature.

3.   A gas becomes more difficult to liquefy the higher its temperature.

4.   He says that in a few years gas will become expensive, and coal will be waiting in the wings as a cheap form of energy.

5.   But as gas has become more available, that is changing.

6.   Gas had become not only relatively inexpensive, but also environmentally friendly.

7.   Given time and sufficient investment, gas should become increasingly competitive with oil.

8.   Over time, however, the Ukrainian gas became harder to exploit, and new Siberian fields proved so rich that the Soviets practically halted investment in Ukraine.

9.   Still, as good as they may get, diesels are unlikely to gain much popularity until gas becomes much more expensive.

10.   The glass-encased gases become restaurant signs, animals, elaborate lettering or anything else you can dream up.