They took millions of years to make, and at some point they will run out. Extracting and transporting them for use has created environmental problems. Cogeneration Oil has become too expensive for most power plants. Coal and natural gas are currently cheap in the US, and are being used more often. Cogeneration is not a new idea, and takes advantage of the way many large electricity users operate.
Many factories use steam in their production process.
Utilities often make and sell steam for these customers, as well as for running their own generators. Recently developed cogeneration plants use new materials and designs to improve reliability, and control both thermal and atmospheric pollution. Since these new technologies are designed into plants from the start, they are less expensive to install. The economy and capability of cogeneration technology allows many plants to return to burning coal without exceeding air-quality standards. Some natural gas plants can produce electricity without steam.