Gas turbine combined cycles are a cost-effective way to use petroleum now. Using advanced high-temperature gas turbines with coal-derived fuels in the future could be even better. Programs are being started to make this happen, even though coal-derived fuels aren't widely available yet. Rules limiting natural gas or oil use in gas turbines could be a problem. Utility companies might have to deal with higher costs and lower efficiency. A possible solution could be using heavy fuels in gas turbines at higher temperatures, which would be cheaper and help with the transition to future fuels.