Natural gas is the preferred fuel for autoproducers, but there have been natural gas shortages in the late 1990s that have forced some of these small
cogeneration power
plants to turn to alternative fuels — not a preferred solution, since most alternative fuels are more expensive than natural gas (on a heat content
basis, including deliver costs to the
plant site) and some alternate fuels (such as heavy oils) have a high sulfur content.