1. Reserves deplete faster than oil (in general)
2. Oil/natural gas ratio: the price of oil divided by the price of natural gas is at an all-time high (or close). This ratio stands at 17 (historically it has been at about an 8 or so). Natural gas prices will go up, oil will decline, or both.
3. Also, natural gas is not a good hedge against the declining dollar (it is for the most part a domestic commodity) and storage capacity is more limited, thus not as admired by speculators as oil. This explains in part why it lagged the the spectacular performance of oil of late.
4. At $4, natural gas it is uneconomical to develop and look for new reserves.
5. No OPEC competition, LNG (liquid natural gas) imports are uneconomical at these prices.
6. Politically more favorable than coal.
7. After emission caps are implemented natural gas will become a cheaper alternative than politically and environmentally unfriendly coal.