Hearings for an inquiry into soaring gas prices in B.C. don't kick off for another week, but several major companies selling gas in the province are already refusing to share details about their profit margins.

The B.C. Utilities Commission (BCUC) asked more than a dozen companies to disclose their retail margins, which show how much money they make per litre of gasoline pumped from their stations.

Shell Canada, Husky Energy, Imperial Oil and Suncor Energy declined the commission's request. In written responses posted online, the companies say those numbers are "confidential" and "commercially sensitive."

"We responded to the BCUC questionnaire. However, some of the questions involve commercially sensitive information, which we must keep confidential," read an emailed statement from Husky.

"Under its governing legislation and the inquiry mandate from the B.C. government, the BCUC was unable to provide an appropriate level of confidentiality for the information. We continue to discuss the issue with the BCUC."

7-Eleven was the only international retailer to hand over its data, but asked the commission to keep the numbers confidential. A version of the company's response posted online had the data blacked out.

Super Save Group also asked that its numbers be kept in confidence.

Gas prices in the Lower Mainland hit all-time highs in April 2019. (Evan Mitsui/CBC)

'Doesn't make sense': economist

Robyn Allan, an independent economist and intervenor in the inquiry, told CBC's The Early Edition host Stephen Quinn she finds it hard to understand why the companies would be reluctant to share confidential or sensitive information with the BCUC.

"It doesn't make sense given that the BCUC is a body that is charged with handling commercially sensitive information all the time," said Allan.

She said not being transparent or accountable about the factors that drive gas prices in B.C. is a "continuation of a theme with these companies."

Allan said there is no cost-based or supply-based reason for these price swings and it's reflective of a lack of competition in the marketplace.

"They've been charging what the market will bear for years," said Allan. "What happened is the public can't bear it any longer."

Sky-high spring prices

B.C. Premier John Horgan ordered the independent inquiry in May, asking the BCUC to look at why prices in the province had skyrocketed in comparison with the rest of the country in recent months.

The premier, who was politically hammered over the issue for weeks, said he wanted to know if price gouging has played a role in high prices.

Prices shot past $1.70 per litre of regular in Metro Vancouver in April, but have been hovering around $1.50 more recently.

A gas station in Surrey, B.C. on April 15, 2019. Super Save Gas revealed its profit margins to the B.C. Utilities Commission, but in a letter, the company asked the commission to kept the numbers confidential. (Evan Mitsui/CBC)

Factors such as global markets, the time of year and the strength of the Canadian dollar can affect the price. There are also more than half a dozen taxes on gas, amounting to 60 cents a litre for drivers in Metro Vancouver.

The province also grapples with a limited supply of gasoline as there are only two oil refineries province-wide.

To make up the difference, the government brings in petroleum from Alberta through the Trans Mountain pipeline or from other countries, including the U.S.

Horgan said the gap between B.C.'s prices and those in other provinces is still too wide, despite those factors.

The BCUC hearings begin in Vancouver next week.