The WSJ has a good article on how the oil and gas industry is converting some of its heavy equipment to natural gas from diesel: "Oil and gas producers such as Apache Corp. and Chesapeake Energy Corp. are driving the shift. After years of promoting the wider use of natural gas as a cleaner, cheaper alternative to petroleum-based fuels, the companies are concluding that natural-gas prices will stay low for years to come, allowing them to save money by substituting it for diesel in their own operations."