The study was conducted by the California Independent System Operator, which oversees the state's massive power grid. Anjali Sheffrin, Cal-ISO's director of market analysis, says some of the money should be refunded to commercial and residential power users, and the rest should be returned to the state's cash-strapped utilities.

According to the report, independent power generators, which sell power to utilities such as Southern California Edison and Pacific Gas & Electric for distribution, manipulated prices in two ways. First, the study says, the generators effectively withheld supplies by demanding excessive prices even though they could have made some money by selling more electricity.

Other times, the ISO says, the generators had power-generation available but did not offer to sell it. Either way, the study concludes, the net effect was to push prices higher.

Spokespersons for the various power generators named in the report either did not return calls from GlobeSt.com or flatly denied the Cal-ISO's allegations. Experts say chances of getting all or even a large portion of the alleged $5.5 billion in overcharges appear slim and would likely involve prolonged court action if a settlement with the providers could not be reached.