Petrol vs diesel: Which is more expensive to own in 2026?
Do you pay more upfront for a cents-saving diesel, or take the hit at the pump with a petrol? As compact diesels are becoming ever harder to find, we plug July’s prices into a baseline model and calculate the exact crossover point where diesel starts making sense. Let’s crunch the numbers.
A firmer hand on production costs, the after-effect of 2015’s Diesel Scandal and a renewed focus on new energy have all resulted in diesel cars becoming an increasing rarity. And that’s a pity, for petrol cars simply can’t match the efficiency of diesel variants.
But, given the recent fluctuations in fuel prices owing to the Middle East conflict, do the latter still make sense today? After some digging, we found an affordable model enabling a reasonable like-for-like comparison to answer the question about petrol or diesel being the most expensive to own.
The price premium: Why do diesel cars cost more upfront in SA?
It is, or was, once the cash-counter’s ultimate car-shopping conundrum: petrol or diesel?
Although sporting known benefits over petrol such as better fuel efficiency and bottom-end tractability, the downside is that diesel cars are pricier because they are more expensive to make.
Diesel engines rely on compression instead of spark to ignite fuel and therefore require sturdier construction of key components. Engine blocks and turbochargers are hardier, while fuel injection and exhaust systems are more specialised. These all hike up the cost of manufacturing.
Such higher production costs destroy the remaining bit of profit margin in these cars. Traditionally, in the small car segment, equivalently priced diesel models were sold in lower trim grades just to be price-competitive against their petrol-powered siblings.
Today, the Kia Seltos LX offers a reasonable platform for a like-for-like comparison, with just R29 000 separating the price of the base-level petrol and diesel versions.
Petrol vs diesel fuel consumption: The real-world efficiency gap in SA
While driver behaviour and road conditions remain significant determinants of fuel consumption, the scientific reality is that the thermal efficiency of diesel engines, along with the energy density per litre of fuel, exceed that of petrol by roughly 10%.
Put into practice, in the case of the Kia Seltos, the diesel derivative consumes an average of 5.2 L/100 km versus 6.3 L/100 km for the petrol model. In a measure of petrol vs diesel consumption, it’s a slam dunk for the latter.
Below, we take these claimed averages for each vehicle and calculate the cost per kilometre using July’s coastal fuel prices by dividing the upfront price premium by the R0.33/km difference, resulting in a breakeven point where the petrol model loses its upfront advantage.
| Metric | Petrol (Kia Seltos 1.5 LX Auto) | Diesel (Kia Seltos 1.5 CRDi LX Auto) | Difference |
| Purchase price | R492 995 | R521 995 | R29 000 |
| Claimed fuel economy | 6.3 l/100 km | 5.2 l/100 km | 1.1 L/100 km |
| July fuel price (coastal) | R26.00/litre | R25.20/litre | — |
| Fuel cost per kilometre | R1.64/km | R1.31/km | R0.33/km |
| Breakeven point | 87 879 km |
The breakeven calculation: How many kilometres are needed to clear the diesel debt?
While petrol wins in the showroom and diesel at the forecourt, to make real sense of the numbers, you need to establish the exact breakeven point where the cumulative diesel savings wipes out the initial purchase price gap.
In the case of the Kia Seltos, that moment arrives just below 88 000 km.
Were you to drive an average of 15 000 km per year, that financial threshold would arrive after 5 years and 10 months. The good news is that the Kia is sold with a 5-year unlimited km factory warranty, meaning that you’ll have peace of mind for most of the duration of closing in on that crossover point.
Beyond the pump: Maintenance & resale value considerations
And the bad news?
Not necessarily bad – yet unquestionably a point you cannot ignore – is the true cost of ownership calculations cannot put aside what happens after the factory service plan has lapsed.
At our projected 15 000 km of mileage per year, the Seltos’ 5-year/90 000 km service plan will see to it that you will reach the 88 000 km breakeven point still fully covered without fear of an expensive mechanical failure.
But thereafter?
It’s worth knowing that diesels are generally reliable long-distance workhorses, but need regular upkeep that’s more expensive than petrol to ensure they run at their best.
That said, your endurance will be rewarded on the day that you decide to sell your diesel Seltos, as its stronger fuel economy and predicted high durability make it command a higher used price than its petrol-powered sibling.
Which to choose, then?
Ultimately, the choice between petrol or diesel is objectively guided by ownership and usage patterns rather than preference for fuel type. For urban, low-mileage drivers looking to change cars every 3 or 4 years, petrol is the most logical and financially sensible bet. You simply won’t cover enough distance to realise the diesel’s up-front premium.
For long-distance haulers and those planning to keep their car for longer than 5 years, diesel is the go-to option. You may pay a little more at every service, but not only do you save every time you fill up, your long-term commitment will also be rewarded come the day you decide to sell.
