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9.04 The cost of fuel


Now that our car is purchased, registered and insured we still have ongoing running expenses necessary to keep it on the road. One of the biggest running expenses is fuel.

In order to manage our fuel expenses, we will need to answer the following questions: 

  • How much fuel does our car use?
  • How much does fuel cost?


Fuel consumption rate

The amount of fuel used by a vehicle is measured as a rate. It is based on the volume of fuel consumed per distance travelled.

Although a variety of units could be used, the industry standard for measuring a vehicle's fuel consumption is litres per $100$100 kilometres.

How fuel consumption is measured

The fuel consumption rate is measured in:

Litres per $100$100 kilometres (L/$100$100 km)

Because fuel consumption tends to fluctuate with speed changes, choosing $100$100 kilometres as the distance, rather than $1$1 kilometre, gives a more reliable measure of fuel consumption. 

In everyday language, the terms 'fuel economy' and 'fuel efficiency' are often used to refer to the average fuel consumption of a vehicle.


Worked example

A 4-cylinder petrol-engine hatchback has a fuel consumption rate of $6.3$6.3 L/$100$100 km.

Calculate the amount of fuel consumed for the following distances travelled:

  1. $5$5 km
  2. $120$120 km



Divide the given fuel consumption by $100$100 to convert from L/$100$100 km to L/km. Multiply this value by the number of kilometres.

  1. Fuel consumed $=$= $\frac{6.3}{100}\times5$6.3100×5
      $=$= $0.063\times5$0.063×5
      $=$= $0.315$0.315 L
  2. Fuel consumed $=$= $\frac{6.3}{100}\times120$6.3100×120
      $=$= $0.063\times120$0.063×120
      $=$= $7.56$7.56 L


Comparing fuel consumption rates

When we decide to purchase a new car, we can use the manufacturer's fuel consumption rates to compare cars and choose the one with the best fuel economy. 

According to Australian standards, car manufacturer's must specify the fuel consumption of their vehicles using three different rates obtained from carefully controlled laboratory tests. Different rates are used to account for the way fuel consumption can vary, depending on driving conditions:

  • The 'urban' rate applies to driving in city environments. It is usually the highest value because a car consumes more fuel when it is constantly changing speed.
  • The 'extra urban' rate applies to driving on highways and freeways. It is usually the lowest value because a car consumes less fuel when driven at constant speed.
  • The 'combined' rate is an overall average for the vehicle's fuel consumption.

Here is an example of fuel consumption rates for a 2018 model 4-cylinder petrol-engine hatchback:

Label Fuel consumption (L/100 km)
Fuel consumption combined $6.3$6.3
Fuel consumption extra urban $5.1$5.1
Fuel consumption urban $8.5$8.5


Fuel consumption labels

Vehicle fuel consumption label

As of April 2009, all new fuel-based cars sold in Australia are required to have a fuel consumption label displayed on their front windshield, prior to sale.

The label indicates the three different fuel consumption rates as well as a rate for the vehicle's average CO2 emissions, measured in grams per kilometre (g/km). 

The Australian government introduced these labels so that consumers are better able to compare fuel consumption and emissions values for different vehicles.

Labels such as this one only apply to vehicles that use fuel. Purely electric vehicles will display a different label.

Because rates on these labels are obtained from laboratory tests, 'actual' fuel consumption in real world conditions may be significantly different. This is due to a range and a combination of factors. 



Factors affecting fuel consumption

The advertised fuel consumption rate for a vehicle will depend on the following factors:

  • Engine size - fuel consumption increases with engine capacity and the number of cylinders
  • Fuel type - diesel tends to be more efficient than petrol
  • Vehicle size/mass - the lighter the vehicle the better the fuel consumption
  • Age of the vehicle - older vehicles tend to have higher fuel consumption rates

Real world fuel consumption is also influenced by the way the car is driven and how often it is changing speed. It may vary according to the following factors:

  • Driving style and behaviour
  • Traffic congestion
  • Quality of the road surface
  • Weather conditions


Fuel for vehicles

The price of fuel is something we have little control over, as fuel prices fluctuate according to supply and demand in global markets.

At service stations, the fuel price is advertised as a rate, based on cents per litre.

How fuel prices are advertised 

cents per litre (c/L)

The two main types of fuel used in Australia are unleaded petrol and diesel, with unleaded petrol being the most common. The popularity of diesel-fuelled cars has grown in recent years, despite a declining trend in other parts of the world due to environmental reasons. 

The use of Liquid Petroleum Gas (LPG) or Compressed Natural Gas (CNG/NGV) in cars has declined significantly in Australia due to increased prices and cuts in government subsidies. It remains a common fuel type in some taxi and commercial vehicle fleets.

The following table shows average fuel prices for service stations across NSW (February, 2019):

Fuel name Ethanol 94 (E10) Unleaded 91 Premium 95 Premium 98 Premium Diesel
Fuel Type unleaded petrol unleaded petrol unleaded petrol unleaded petrol diesel
Price (c/L) $124.3$124.3 $129.5$129.5 $141.7$141.7 $147.7$147.7 $142.7$142.7

Consumers can use the NSW Fuel Check website (or app) to monitor fuel prices in their area and help them decide on the best times or locations to fill their car's fuel tank. 



Worked example

A 4-cylinder petrol-engine SUV (Sport Utility Vehicle) has an 'urban' fuel consumption rate of $8.3$8.3 L/$100$100 km and a fuel tank capacity of $48$48 litres.

  1. Calculate the amount of fuel consumed travelling $90$90 km in an urban environment.
  2. How far could the vehicle travel on half a tank of fuel? Answer to the nearest kilometre.
  3. If the current price of fuel is $130.3$130.3 cents per litre, calculate the cost of filling an empty tank.



  1. Divide the given fuel consumption by $100$100 to convert from L/$100$100 km to L/km. Multiply this value by the number of kilometres.
    Fuel consumed $=$= $\frac{8.3}{100}\times90$8.3100×90
      $=$= $0.083\times90$0.083×90
      $=$= $7.47$7.47 L
  2. The car has a fuel tank capacity of $48$48 litres, so half a tank is $24$24 litres. We know that the car can travel $100$100 km using $8.3$8.3 L of fuel. To find how far it travels on $1$1 L of fuel, we divide $100$100 by $8.3$8.3. This gives us a value in km/L. We multiply this value by $24$24 to find the distance travelled using $24$24 L.
    distance travelled $=$= $\frac{100}{8.3}\times24$1008.3×24
      $=$= $289.156$289.156...
      $=$= $289$289 km
  3. First convert $130.3$130.3 c/L to $1.303$1.303 $/L by dividing by $100$100. Multiply this by the capacity of the fuel tank in litres.
    Cost to fill tank $=$= $\frac{130.3}{100}\times48$130.3100×48
      $=$= $62.544$62.544...
      $=$= $\$62.54$$62.54


What about electric vehicles?

Petrol and diesel are based on non-renewable fossil fuels. When used in vehicles, they produce greenhouse gas emissions like CO2, and other potentially harmful pollutants. One of the most promising alternatives for reducing these emissions is electricity stored in on-board rechargeable batteries.

  • Petrol-electric hybrid vehicles have been available in Australia for some time. They are powered mainly by a petrol engine that is supplemented by electricity supplied from a battery. They don't have to be 'plugged-in' for recharging as the car itself recharges the battery when it is moving. These vehicles usually have lower fuel consumption rates than petrol-only engines. Diesel-electric hybrids are also available.
  • Plug-in Hybrid Electric Vehicles (PHEV) are more recent. They are powered mainly by an electric motor that is supplemented by a petrol or diesel engine. These vehicles require 'plug-in' charging but have very low fuel consumption rates and reduced emissions. 
  • Battery Electric Vehicles (BEV) are more recent still. They are powered completely by an electric motor and rechargeable batteries. These vehicles require regular 'plug-in' charging and have zero emissions.

While newer hybrid and pure electric vehicles have recently started selling in Australia, they are still relatively expensive and not widely available. This is expected to change as demand increases and battery technology improves.


Practice questions

Question 1

Yvonne's car has a fuel consumption of $8$8 L/$100$100 km.

Her car's fuel tank can hold $65$65 litres of petrol.

  1. How far can the car travel on $1$1 L of petrol?

  2. Yvonne is driving on the freeway and notices that her fuel tank is $\frac{1}{4}$14 full.

    How much further can she drive on the amount of fuel she has remaining?

Question 2

Answer the following questions:

Petrol Type Price (c/Litre)
Unleaded $120.9$120.9
Diesel $164.1$164.1
E10 Unleaded $114.7$114.7
  1. A V6 car consumes $13$13 L/100 km and runs on unleaded fuel. Calculate the cost for a $60$60 km trip in dollars, writing your answer to 2 decimal places.

  2. A 4-cylinder car consumes $8.7$8.7 L/100km and runs on E10 Unleaded. Calculate the cost for a $80$80 km trip.

  3. A V8 car consumes $14.5$14.5 L/100km and runs on diesel fuel. Calculate the cost of a $70$70 km trip.

Question 3

The prices of unleaded petrol (in c/L) for three different locations are given below.

  Mon Tues Wed Thurs Fri Sat Sun
Perth $125.6$125.6 $133.2$133.2 $122.7$122.7 $142.1$142.1 $140.2$140.2 $133.3$133.3  $123.8$123.8
Canberra $149.9$149.9 $119.5$119.5 $144.3$144.3 $113.3$113.3 $134.2$134.2 $131.4$131.4 $128.8$128.8
Sydney $146.7$146.7 $124.8$124.8 $114.6$114.6 $130.2$130.2 $121.9$121.9 $120$120 $142.2$142.2
  1. What is the daily average petrol price for Sydney?

    Round your answer to two decimal places.

  2. In Canberra, what is the difference in price for filling a $50$50 litre tank on Monday compared to on Sunday?

    Give your answer in dollars, and round your answer to the nearest cent.

  3. Tom filled his tank of petrol in Canberra on Sunday.

    If his rate of fuel consumption is $9.7$9.7 litres/$100$100 km and his car travelled $515$515 km on the one tank, what was the cost to fill his car with petrol?

    Write your answer in dollars, rounding to the nearest cent.



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