Important is that 6 mcf (6000 cf of NG) has the same energy content a one barrel of oil. At today's prices -Oil at $98.99 and NG at $3.58 per mcf- makes oil 98.99)/(3.58x6) 4.6 times more expensive than NG, based on the same energy content. Back in 2008 when oil was over ~$140, NG was about ~$13.50 or 140/(13.5 x6), or ~1.7 times NG based on the same energy content. Then there was the spike attributed to Enron years earlier.
If the price per energy content were equal for both today, NG would sell for ~$16.50 today, even at half that price, it could be a serious blow too NG use and effect its sales.