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.
More top news
Jimmy Sinclair, who has waited his whole life to vote for independence, told us he was "disappointed" after the 'No' vote.
Photos from an historic day in Scotland's history as voters choose to remain part of the United Kingdom.
Is Manchester really more powerful than Wales and Northern Ireland? Find out how the union's four nations compare with England's regions.