MPs have made a series of recommendations to energy companies, including making energy bills easier to understand and for prices to be compared with those of other companies, after they warned that "trust" was "eroding".
There were "serious shortfalls" in the way energy companies communicated with customers, although improvements have been made, said the report.
Speaking on behalf of the committee, Liberal Democrat MP Sir Robert Smith said:
At a time when many people are struggling with the rising costs of energy, consumers need reassurance that the profits being made by the Big Six are not excessive.
Unfortunately, the complex vertically integrated structure of these companies means that working out exactly how their profits are made requires forensic accountants.
Ofgem should shine a brighter light on the internal structure of these big companies.