It was the Chinese who first drilled an oil well in the 4th century using bamboo poles, so that they could heat sea water to derive salt. The petroleum industry was started when Edwin Drake drilled an oil well in Texas in 1859 for the Seneca Oil company. Some decades later the word petrol came into use to describe the liquid gold has become vital to our existence today. Over the years, the severe pressure of demand on petrol has made it undergo many changes with a wide variety of variants being developed.

Octane rating is an important characteristic of petrol. Without invoking the ghost of high school organic chemistry too much, let me just quickly explain what octane means and why it is important to petrol. When crude oil is broken down in a refinery, you end up with hydrocarbon chains of different lengths—methane, butane, etc. Octane is the one with eight hydrocarbons chained together. A better octane rating means better petrol quality.

Inside a car engine, sometimes the mixture of fuel and air combusts due to compression, before the engine’s spark plug can ignite it. This causes knocking—the loud rumbling sound from the hood and the jolts you experience when you are maybe, climbing an uphill path. Knocking is very bad mechanically for the engine. Octane prevents knocking because it facilitates compression. Higher the octane content, more the fuel can get compressed and wait for the spark plug to combust it, instead of exploding on its own. That’s why higher octane fuels burn more slowly and efficiently while lower octane ones are erratic and volatile.

Hence the quest by petrol companies to improve the octane rating of petrol. During World War I, octane amounts were boosted by adding a lead compound called TEL. Cheaper versions of gasoline started getting by with the addition of TEL and led to the production of leaded petrol. The toxic effect of lead emissions caused them to be banned in 2000.

Since then, we have unleaded petrol, which is plain-vanilla petrol with an octane of 87-89. If you want more pumped up petrol in India, there’s Speed from BPCL (Speed 93, 97), Power from HP and Extra Premium from IndianOil. All are positioned as petrol having additives which clear harmful deposits from the engine and thereby provide longer engine life, with ancillary benefits of more mileage and better pickup.

Is high-octane fuel for everyone?

But here’s the rub. William Green, a chemist in MIT, reveals in an article in Scientific American that not all cars need high-octane fuel to prevent knocking. Some car engines can behave just as well with regular petrol. Which means you don’t have to spend on premium fuel in all cases.

Cars have different compression ratio, which is fixed by the designer of the car engine. If that ratio is in the neighbourhood of 8 to 1, (Santro Zip, New WagonR), then petrol with an octane of a mere 87 will hold just as fine. Regular fuel will burn just as properly as premium fuel. High performance engines in SUVs, heavier vehicles and those with turbochargers, however, need high octane fuel to prevent knocking.

So when Rahul Bhardwaj, senior vice-president of a credit company in Mumbai, buys premium petrol for his Scorpio with an engine compression ratio of 18:1, it’s the right decision. He buys high-octane petrol because he assumes that it is somehow better for his car’s health than normal petrol and thinks it does give higher mileage, at least on the highway.

Anil Bijlani, general secretary of the Delhi Petrol Dealers Association, agrees. He advises tanking up on premium fuel once in three times. “This will clear out the injectors and your trips to the service station reduce." I asked him if it improves mileage and he said, “It does to the extent that the harmful deposits would have reduced performance and the high-octane petrol will clean it up and bring it to its peak once again."

It’s clear that high-octane petrol does good stuff to the car, especially when the car is designed for it.

At what price point

But premium fuels are priced about Rs2.50 extra per litre. At that price, is it worth it? “No," says Bijlani without hesitation. “When these fuels were introduced in 2002, they were about 50 paise more per litre, which made sense. Even if it was Rs1 more per litre, customers would be tempted. Now, at a price point of Rs2.25-2.50 per litre, volumes are decreasing."

Ankush Bansal, a batchmate whose family has been in the petrol business for decades was secretary of the Indian Oil Petrol Dealers Association in Delhi. He thinks the extra money is not worth it. “If you buy a bottle of the additive from the petrol pump and add it to your normal petrol, your cost per litre would be just 15-20 paisa per litre," he says.

For those who are convinced that it’s worth it, they still have to deal with the issue of limited availability. In Delhi, Speed 97, for instance, is available only in a few petrol pumps around the extreme upmarket diplomatic enclaves of Chanakyapuri and Golf Links. Bhardwaj finds it difficult to procure Power or Speed in Mumbai. “It seems randomly unavailable in Andheri and Bandra," he says.

Then of course there are those who are not convinced. When I ask my driver Suresh if we should try premium fuel to improve the mileage, he says in his characteristic earthy wisdom, “Woh bas ek vehem hai (It’s just a delusion)." There are lots of Sureshs on Indian roads. Perhaps that’s why the sale of premium petrol in India is only 10% of total petrol sales.

Vandana Vasudevan writes stories of mass urban consumer experiences. She is a graduate from the Indian Institute of Management, Ahmedabad, and works with HT Media Ltd.