CNG vs Petrol in Nigeria: Is It Really Cheaper? What Research Says About Cost, Efficiency and Payback
A systematic review of 20 studies carried out by a group of researchers reveals where CNG beats petrol, where petrol still has the upper hand—and what the findings could mean for you and other motorists struggling with high fuel costs.
In an era of high petrol pump prices, motorists and car owners are searching for alternatives. Meanwhile US-Iran conflict continues unabated and the prices of petroleum products refuse to yield ground to their upward movements. In their wake, people all over the world are left grappling with the ripple effects in the form of high cost of energy and high cost of essential food items.
For many people in developed countries, one answer readily comes to mind: ditch the petrol vehicle and buy an electric car.
But that solution is not equally available everywhere.
Electric vehicles remain expensive and, for many middle-class motorists in developing countries, are still beyond easy reach. That leaves millions of drivers looking for something more immediate—something that can reduce fuel costs without requiring them to replace the entire vehicle.
And that is where compressed natural gas, better known as CNG, enters the conversation.
CNG has been around for quite a while and has increasingly been presented as a practical alternative to petrol for motorists. In Nigeria, where the price of petrol has become a major household and business expense, the attraction is obvious.
If you can convert the vehicle you already own and then spend less on fuel, why wouldn’t you?
But there is a more important question.
Is CNG truly a cheaper alternative to petrol when fuel cost, conversion cost, engine performance, efficiency and access to refuelling stations are taken into account?
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And what does research actually say about all these?
A systematic review carried by a group of researchers—Joyce Longtang Daser-Adams, Nehemiah Shola Ibitoye, Elijah A. Alhassane, David Ayodeji Olasehinde, Matthew Folorunsho Amodu, Oluwaseyi Matthew Abioye, Daniel Damilola Ibitoye, and Olatunde A M Onakoya—comparing petrol and CNG vehicles provides some useful answers.
Researchers found that CNG can burn cleaner, use fuel more efficiently under several operating conditions and cause less deterioration inside an engine. Petrol, however, generally produces more power and torque.
In other words, switching fuels is not as simple as choosing between expensive petrol and cheap gas.
There are trade-offs.
The researchers reached that conclusion after a systematic review that began with 178 studies. After duplicates were removed and the papers were screened, 45 went through full-text assessment. Only 20 studies ultimately met the criteria for inclusion.
And what those studies found could matter to anyone in Nigeria and other climes thinking about converting a petrol vehicle to CNG.
What happens to your engine when you switch from petrol to CNG?
Believe it or not, one of CNG’s biggest advantages starts with something most motorists rarely think about: octane.
What exactly is octane?
Octane tells you how well a fuel can resist knocking inside an engine.
Engine knocking happens when the fuel-air mixture starts burning at the wrong time instead of burning smoothly after the spark plug fires. When that happens repeatedly, the engine can lose efficiency and experience extra stress.
The higher the octane rating, the more resistant the fuel is to this unwanted combustion.
Petrol generally has an octane rating of around 87 to 98, while the review reports the octane in CNG at approximately 120 to 130. That higher rating allows CNG to tolerate higher compression before knocking becomes a problem.
Think of it this way: octane does not tell you how much power a fuel contains. It tells you how resistant the fuel is to igniting prematurely under pressure which can overtime quietly reduce the efficiency of your engine.
So a higher octane number does not automatically mean a faster car.
And that distinction matters with CNG.
Because although CNG has a higher octane rating, petrol still generally produces more power.
With the use of CNG, there is a lower brake torque.
What does brake torque mean? Brake torque is the twisting force produced by an engine. It is the force that helps a vehicle move away from a standstill, climb a hill, carry a heavy load or accelerate when you press the pedal.
A vehicle with more torque usually feels stronger when pulling.
Imagine trying to loosen a tight wheel nut with a spanner. The twisting force you apply is torque. Inside a car engine, the same basic principle applies. Combustion creates a turning force that rotates the engine and eventually drives the wheels.
The word “brake” in brake torque comes from the way engine output is measured on testing equipment known as a dynamometer. It does not mean the vehicle’s braking system.
The studies reviewed repeatedly found lower torque when engines are operated using CNG instead of petrol.
One experiment found that CNG reduced brake torque by 12.7% and brake power by 12.4% compared with gasoline. Another study involving similar Honda Civic vehicles reported a 21% fall in peak power and a 17% fall in peak torque.
Another found CNG produced 18.5% less power.
For the driver, that could mean a CNG vehicle may feel less responsive during hard acceleration or when carrying heavy loads, or when climbing a hill, depending on the engine and how the CNG system is configured.
Why?
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CNG is a gas, so it behaves differently as it enters an engine. Its lower volumetric efficiency can reduce the density of the intake charge and ultimately restrict the amount of power the engine produces.
Petrol does not have that problem to the same degree.
Its higher energy density helps explain why petrol vehicles tend to deliver the acceleration and power drivers have become accustomed to.
But power is only one part of the story.
CNG Is more thermal efficiency under particular operating conditions
What is thermal efficiency?
Thermal efficiency tells you how effectively an engine converts the energy contained in fuel into useful mechanical work.
Not all the energy in fuel actually moves the car.
A large portion is lost as heat through the engine, exhaust and cooling system.
So if two engines burn fuel containing the same amount of energy, the engine with the higher thermal efficiency converts more of that energy into useful power and wastes less of it as heat.
The review notes that conventional gasoline engines can have thermal efficiency of around 25% to 30%. That means much of the energy in petrol is lost instead of being converted into useful movement.
Several of the reviewed studies found advantages for CNG in thermal efficiency under particular operating conditions.
One study reported that CNG had 5.4% higher thermal efficiency than gasoline. Another found higher brake thermal efficiency with CNG at 80% throttle.
So when researchers say CNG can be more thermally efficient, they are essentially saying that under the conditions studied, the engine was able to get more useful work from the energy supplied by the fuel.
Does CNG actually use fuel more efficiently?
This is where things get interesting.
The review found that CNG can perform strongly in thermal efficiency and brake-specific fuel consumption.
Brake-specific fuel consumption, usually shortened to BSFC, measures how much fuel an engine uses to produce a given amount of power.
A lower BSFC is generally better.
It means the engine needs less fuel to produce the same amount of useful output.
But comparisons must be made carefully because petrol is a liquid while CNG is a gas, and the fuels are stored and sold differently.
One study reported that CNG had 17.2% lower brake-specific fuel consumption than high-octane gasoline.
Another found higher brake thermal efficiency with CNG.
For Nigerian motorists, however, engine efficiency is only part of the question.
The bigger issue is whether that efficiency eventually translates into lower naira spending.
And according to the review, it can.
The literature review cites studies suggesting that CNG can reduce fuel costs by approximately 30% to 50% compared with petrol.
For someone who spends heavily on petrol every month, that difference can be substantial.
But there is another benefit that may not show up immediately at the filling station.
CNG combustion leaves fewer residues inside an engine.
Natural gas burns more cleanly than petrol and produces fewer carbon deposits on components such as spark plugs and valves. According to the review, that can reduce wear, slow deterioration of lubricating oil and potentially extend engine life.
One study went further.
When researchers compared CNG with high-octane gasoline over 120 hours of operation, they found slower deterioration in viscosity, flash point and total base number in the lubricating oil used with CNG.
Wear particles also fell.
Iron particles were 13.8% lower, copper 37.7% lower, chromium 30% lower and aluminium 29.1% lower.
That is the kind of difference motorists may never see from behind the steering wheel—but could eventually notice in maintenance.
So CNG is easier on an engine?
The research suggests it can be.
But there is a catch.
The same fuel that may reduce engine wear can also leave drivers with less power.
For someone whose priority is urban commuting, fuel efficiency or lower operating costs, that trade-off may be acceptable.
For someone who needs maximum acceleration, high torque or demanding performance, petrol retains an advantage.
And this is where the decision becomes much clearer.
Should a motorist convert to CNG?
Do not begin with the question: “Is CNG cheaper?”
Begin with five practical questions.
First: How much do you currently spend on petrol every month?
The more petrol you consume, the greater the potential financial benefit from switching to a cheaper fuel.
A motorist spending ₦30,000 a month on petrol and another spending ₦300,000 a month face completely different conversion economics.
Second: Is CNG reliably available along the routes you normally travel?
This can be more important than the price difference.
The review cites a huge gap between Nigeria’s established petrol network and its much smaller CNG refueling network. One estimate cited roughly 33,000 petrol stations, compared with just 14 CNG stations reported in 2023, although additional CNG infrastructure was subsequently being developed.
If your nearest reliable CNG station requires a major detour, some of your apparent fuel savings may disappear through extra distance, time and inconvenience.
Third: What type of driving do you do?
A high-mileage taxi, ride-hailing vehicle, delivery van or company fleet may recover conversion costs faster because it consumes more fuel.
A privately owned car used mainly for short weekend journeys could take much longer.
Fourth: How important is maximum engine power to you?
The review repeatedly found lower power and torque with CNG in conventional or converted engines.
Drivers who mainly commute in urban traffic may consider that acceptable.
Drivers whose vehicles frequently carry heavy loads, operate at high speeds or require maximum acceleration need to pay closer attention to the performance trade-off.
Fifth: How long do you intend to keep the vehicle?
This may be the most overlooked question.
If conversion costs ₦1.5 million but you plan to sell the vehicle next year, you may never recover the investment through fuel savings.
If the vehicle will remain in service for several years and travels long distances every day, the mathematics can change substantially.
The practical CNG payback calculation
This is the calculation every Nigerian motorist or business should perform before converting.
Start with your real petrol spending.
Monthly petrol cost = Average litres used per month × Petrol price per litre
Then estimate what the same driving pattern would cost using CNG.
Monthly CNG cost = Estimated CNG consumption for the same distance × CNG price
Then calculate:
Monthly fuel saving = Monthly petrol cost − Monthly CNG cost
After that:
Simple payback period = Total conversion cost ÷ Monthly fuel saving
The result tells you approximately how many months of fuel savings are required to recover the amount spent on conversion.
Here is a simple illustration.
Assume a motorist currently spends:
₦250,000 per month on petrol.
Suppose operating the vehicle on CNG reduces the fuel bill by 40%.
That sits within the 30% to 50% fuel-cost saving range cited in the review.
At a 40% saving:
₦250,000 × 40% = ₦100,000 monthly saving.
If conversion costs ₦1.5 million:
₦1,500,000 ÷ ₦100,000
= 15 months.
The simple payback period would therefore be about 15 months.
After that point, continued fuel savings would begin to exceed the original conversion cost, assuming prices, usage and performance remain broadly similar.
But the calculation should not stop there.
A more realistic Nigerian payback test
Drivers should also include the additional costs created by the switch.
Adjusted monthly saving = Petrol cost avoided
− CNG fuel cost
− additional travel cost to reach CNG stations
− additional maintenance or inspection costs
− any financing cost attached to the conversion
Then:
Adjusted payback period = Conversion cost ÷ Adjusted monthly saving
Suppose the same driver saves ₦100,000 in fuel each month but spends an additional ₦15,000 monthly because reaching a CNG station requires extra driving and time-related costs.
Adjusted saving:
₦100,000 − ₦15,000 = ₦85,000.
Payback:
₦1,500,000 ÷ ₦85,000 = about 17.6 months.
That is already nearly three months longer than the simple calculation.
And conversion cost matters enormously.
The review cites Nigerian reports putting conversion costs at around ₦1.5 million in one estimate and as high as about ₦2.5 million in another.
At ₦100,000 monthly savings:
A ₦1.5 million conversion takes about 15 months to recover.
A ₦2 million conversion takes about 20 months.
A ₦2.5 million conversion takes about 25 months.
That is why asking only whether CNG is cheaper per unit of fuel is not enough.
The real question is how long the savings will take to recover the conversion investment.
A clearer decision guide
For a Nigerian motorist, CNG may make stronger financial sense if you drive long distances every month, spend heavily on petrol, have a reliable CNG station close to your normal route and intend to keep the vehicle long enough to recover the conversion cost.
It may also be more attractive to taxi operators, ride-hailing drivers, delivery businesses and companies operating fleets because high fuel consumption can allow the initial conversion cost to be recovered faster.
Petrol may remain more practical if your mileage is low, your monthly petrol bill is relatively small or you regularly travel through areas where CNG is difficult to find.
The same applies if your vehicle is used for work that depends heavily on strong acceleration, torque or sustained high-load performance.
And there is a third category.
For some motorists, the answer may simply be “not yet.”
The economics of CNG can look attractive on paper while infrastructure still makes actual ownership inconvenient.
That means a Nigerian driver may reasonably conclude that the fuel savings are attractive but that the CNG station network around his home, workplace or usual travel route is not yet adequate.
As infrastructure expands, that calculation can change.
So CNG is not automatically a good or bad financial decision.
It is a capital-investment decision.
You spend money today converting a vehicle in exchange for expected fuel savings over future months and years.
And like any investment, the important question is not merely whether one fuel is cheaper.
It is whether the savings are large enough—and available consistently enough—to recover what you spent on conversion within the period you expect to continue using the vehicle.
CNG Produces Less Pollution Than Petrol—but Researchers Found One Important Exception
The biggest environmental argument for CNG looks convincing until engine speed and load start to rise
If you compared the exhaust from a petrol-powered vehicle with one running on compressed natural gas, you might expect one fuel to come out as the obvious winner.
For several pollutants, it does.
The systematic review found that CNG generally produces substantially lower carbon monoxide, carbon dioxide and hydrocarbon emissions than petrol.
In one of the studies examined, carbon monoxide emissions fell by 89.7% when the engine operated on CNG. Carbon dioxide emissions were 12.1% lower, while hydrocarbon emissions also dropped substantially.
Another study found CNG reduced hydrocarbons by 59.7%, carbon monoxide by 43.6% and carbon dioxide by 19%.
That sounds like a clear environmental victory.
But there is one pollutant that complicates the picture: nitrogen oxides, or NOx.
Why does CNG produce less pollution?
CNG is made predominantly of methane, which accounts for about 85% to 96% of its composition.
Methane has a high hydrogen-to-carbon ratio, helping CNG produce less carbon dioxide for each unit of energy generated. It also combusts with fewer residues and pollutants than petrol.
Several studies cited in the review put the reduction in carbon dioxide from CNG combustion at roughly 20% to 25% compared with petrol and diesel.
That difference becomes important when millions of vehicle journeys are involved.
The review also cites evidence from public transportation showing that the introduction of CNG contributed to a 31% reduction in air pollutants in one setting in China.
Carbon monoxide tells a similar story.
Petrol engines can produce higher CO levels when combustion is incomplete. CNG repeatedly showed lower CO emissions across the studies examined.
Hydrocarbons followed much the same pattern.
Because CNG burns more completely, fewer unburned hydrocarbons can escape in the exhaust.
So what is the problem with NOx?
Temperature.
Under low-load conditions, some studies found that CNG produces lower nitrogen oxide emissions than petrol.
Push the engine harder, however, and the picture can change.
As engine load and speed rise, combustion temperature can increase. Higher combustion temperatures encourage the formation of NOx.
One study found CNG NOx emissions were 41% higher than petrol at 50% throttle and 38% higher at 80% throttle.
Other studies in the review also recorded increases in NOx under high-speed or high-load operation.
That means saying simply that CNG “produces fewer emissions” misses an important detail.
For carbon monoxide, hydrocarbons and carbon dioxide, CNG generally has the advantage.
For NOx, operating conditions matter.
The researchers argue that engine design and tuning therefore become particularly important if CNG is expected to deliver lower emissions across different speeds and loads.
But emissions are not the only obstacle facing CNG drivers in Nigeria.
There is the question of money.
Is CNG really cheaper than petrol?
The review cites studies suggesting that CNG can reduce fuel costs by approximately 30% to 50% compared with petrol.
For motorists driving long distances—or businesses operating fleets—that could add up quickly.
But first, the vehicle has to be able to use CNG.
And conversion can be expensive.
The review cites Nigerian reports putting conversion costs as high as about ₦1.5 million in one estimate and around ₦2.5 million in another. The exact amount varies with vehicle type, region and available support.
That means a driver may have to spend a substantial amount upfront before benefiting from cheaper fuel.
For lower-income motorists, that initial cost can become the very thing that prevents them from accessing the savings CNG promises.
Then comes another practical question: Once you convert your car, where do you refill it?
This may be CNG’s biggest everyday problem
Petrol has an advantage that has nothing to do with chemistry.
It is everywhere.
The review cites an estimate of roughly 33,000 petrol filling stations in Nigeria. By comparison, a 2023 report cited put the number of CNG stations at just 14, though additional stations were subsequently being developed.
That gap changes the experience of owning a CNG vehicle.
A petrol driver can generally expect to find fuel across urban areas, rural communities and major highways.
A CNG driver may have to plan.
For long-distance commercial vehicles, the problem becomes even more serious. The review notes that truck operators and logistics companies can be reluctant to adopt CNG when reliable refuelling stations are not available along the routes they travel.
No matter how cheap a fuel is, it becomes less useful when motorists cannot conveniently find it.
The authors suggest that installing CNG pumps at existing petrol stations could help close that gap.
So which fuel comes out ahead?
The research does not produce one answer for every driver.
CNG delivers lower CO, CO₂ and hydrocarbon emissions. It offers strong knock resistance, good thermal efficiency, lower brake-specific fuel consumption in many operating conditions and signs of reduced engine wear.
But CNG also tends to produce less power and torque. NOx emissions can rise under heavy load and high-speed operation. Converting a vehicle can require a substantial upfront payment, and Nigeria’s refuelling infrastructure remains far less extensive than the petrol network.
Petrol turns those strengths and weaknesses almost upside down.
It delivers greater power, stronger acceleration and the convenience of established infrastructure. But it generally performs worse on several emissions measures examined in the review.
That is why the researchers ultimately describe fuel choice as a balance between performance, environmental impact and the requirements of the particular vehicle or user.
For Nigerians confronting high petrol prices, that may be the most useful way to look at CNG.
It is not simply a cheaper fuel.
It is a different fuel with a different cost structure, different performance characteristics and different infrastructure requirements.
So before converting, the question is not merely, “How much cheaper is CNG than petrol?”
It is how much do I spend on petrol now, how much will I actually save with CNG, what will conversion cost me, where will I refill, how will my vehicle perform—and how many months will it take before I get my money back?
What is your take: will you convert to CNG?
