Even after a revision following a mistake with a price calculation, diesel will still be at a record-high level from midnight, breaching R30 for the first time.

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A decimal point error has mistakenly increased South Africa’s official wholesale diesel price for May by almost R1 a litre.

The Department of Mineral and Petroleum Resources announced on Monday that wholesale diesel prices would increase by almost R6.19 a litre on Wednesday.

This was incorrect because it subtracted only 0.93c from the diesel fuel levy instead of 93c.

In April, to support the economy amid a fuel price shock, government cut the diesel fuel levy by R3 a litre.

In May, this relief increased by 93c to R3.93.

But in its calculation for the May diesel price, the department’s calculation accidentally accounted for a change of 0.93c, not 93c.

This means the diesel price should rise by R5.27 a litre – 92c less than the official increase.

An official from the department has confirmed the mistake and said that stakeholders were informed on Tuesday morning.

An updated release from the Central Energy Fund on Tuesday shows that diesel wholesale prices will be R31.18 in Gauteng and R30.30 on the coast from Wednesday, not R32.10 and R31.22, respectively, as previously announced.

Even after the correction, diesel prices will rise to a record high from midnight, breaching R30 for the first time.

The Iran war has triggered a fuel price shock, with the average Brent crude oil price at $101 over the past month, from below $65 in January. The closure of the Strait of Hormuz and damage to key infrastructure are throttling fuel supplies.

Diesel prices have been disproportionately affected by higher international demand and a shortage of diesel refinery capacity.

READ | EXPLAINER | Why the diesel price is skyrocketing – more than oil, petrol

With a price hike of R3.27 a litre on Wednesday, petrol prices will be pushed to their highest level in almost four years.

The price of 95 unleaded petrol will be R26.63 in Gauteng and R25.76 in coastal regions.

A large slate levy of almost R1.23 a litre this month has partly offset continued fuel levy relief on petrol and diesel.

The slate account is used to pay fuel importers for the difference between the regulated fuel price they are allowed to charge and the actual price they pay to import or manufacture fuel during that month, which varies daily on international markets and is also affected by the fluctuating rand-dollar exchange rate. A slate levy must be paid when the account is more than R500 million in the red.

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The government plans to halve the general fuel levy relief in June, before it is phased out and restored to pre-war levels in July.