Subsidiaries of global oil giants Chevron, Shell, Total and BP were referred to South Africa's top anti-trust body Wednesday over accusations they have been colluding to rig consumer prices since the 1980s, with a recommendation that the companies face massive fines.

Following "wide-ranging investigations" since 2009, the Competition Commission said it had uncovered "collusive conduct" that stretched back decades, and had referred the case to the Competition Tribunal for judgement.

The commission recommended that each company be fined 10 percent of total turnover from their South African business for the last financial year.

"The investigation revealed collusive conduct through extensive exchanges of commercially sensitive information by the respondent oil companies," it said.

The information was said to include detailed monthly sales figures and collusion to influence the regulatory environment.

The products included petrol, diesel, kerosene, heavy furnace oil, bitumen, liquid petroleum gas and lubricants, and specific grades within these categories.

"The oil companies intended, inter alia through the information exchange, to protect historically high profit margins."

Since 2005 the firms were accused of rigging prices via South African Petroleum Industry Association (SAPIA), an industry lobby group.

Domestic companies Sasol and Engen were also accused.

Anglo-Dutch major Shell said it would "review the Commission's referral and take a decision on our next steps."

"We have cooperated fully with the Commission's three year investigation and we are committed to conducting our business in a manner that is both fair and ethical," it said in a statement.

"As a matter of policy, Shell prohibits anti-competitive conduct. It is against our general business principles, code of conduct and company values.

We will review the Commission's referral and take a decision on our next steps."

Sasol said a 2010 internal review had shown no wrongdoing.

"No evidence was found to support the allegations we note in the Commission's media statement," it said in a statement.

Other companies and SAPIA could not be reached for comment.

The price of fuel is a politically tinged subject in South Africa.

On Wednesday the government reported a 5.5 percent year-on-year increase in prices in September, largely due to an increase in the cost of petrol.