Africa's biggest economy would be hard-pressed to fill the gap quickly.

Only Turkey and Sri Lanka rely more heavily on Iran for oil.

"We have said let's work on a worst-case scenario. In other words, let's just assume that we cannot get anything out of Iran, or at a reduced rate, what is going to be the impact?" Nelisiwe Magubane, director-general of the Department of Energy, said yesterday.

The EU banned imports of oil from Iran and imposed a number of other economic sanctions on Monday, joining the US in new measures against that country.

Magubane said most South African refineries were designed to treat Iranian crude and that an adjustment to handle other crudes would be costly.

"It is clear that it is going to cost the South African motorist because the refineries might need to do amendments to have a different crude oil diet," she said.

Magubane said talks involving the Presidency and the Treasury would be held on how to minimise the effect of a change in Iranian oil imports, and that alternative sources were under consideration.

US Deputy Secretary of Energy Daniel Poneman said during his visit to South Africa that Washington had been in talks with all oil importers to find alternatives to Iranian supply and would work to avoid price shocks.

South Africa and Iran have significant investment links.

MTN Group, Africa's biggest telecoms company, is a major player in Iran, where it has over 32 million subscribers and makes nearly 10% of its revenue.

Petrochemicals group Sasol said in November that it had entered talks to about divesting itself of its operations in Iran. The group, which has a US listing, said in a filing to the US Securities and Exchange Commission that there was a risk that sanctions would be imposed on it by the US, the EU and the UN as a result of its investments in Iran.

Sasol spokesman Jacqui O'Sullivan said yesterday that talks were continuing with businesses and government stakeholders.

"In view of recent developments regarding trade restrictions and possible oil sanctions against Iran, Sasol Oil is diversifying its crude oil sourcing to mitigate risks associated with oil supply disruptions from the Middle East."