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Path360 lower viscosity lubricants fuel saving


Most gasoline and a significant portion of diesel sold globally is used in passenger cars.  The engine oil used in car engines influences their efficiency; lower viscosity oils generally enable reduced fuel consumption for a given distance travelled by a vehicle.  Castrol, BP’s automotive lubricants business sells a broad portfolio of engine oil products – this portfolio is biased towards lower viscosity options as a consequence of its technology development, route to market, countries where we operate and relationships held with major automotive OEMs. Consequently, on average, engines using BP engine oils will consume less fuel than they would if using industry-average engine oil.


A low viscosity engine oil is relative to the typical grade of engine oils sold in that market. Defining what is a low viscosity engine oil in terms of specific grades will differ from market to market. In the context of this methodology we are considering the impact of a portfolio of lubricants used in cars around the world which are predominantly lower in viscosity grade than the global average portfolio. For example the bp 2019 lubricants portfolio consisted of 8% 0W-20 sales vs the global inducts lubricant sales of 4%.


Castrol has developed the following methodology for identifying annual (shown  here for 2019) fuel savings attributable to use of Castrol engine oils in cars.   Although our methodology uses industry standard tests this is a calculation methodology developed by Castrol for our own use.


Determining fuel consumed

Given the above premise, it was first necessary to determine how much gasoline and diesel was consumed in passenger car engines using a portfolio of engine oils with a viscosity mix equal to that of the global industry average.  This requires some source data and some assumptions:



  • Global gasoline consumption from BP Statistical Review 2019:

  • European passenger car total CO2 output:  to determine the volume of diesel consumed in the EU-28 by passenger cars



  • This is a performance improvement claim as opposed to a full life-cycle assessment.
  • All gasoline sold goes into cars
  • Calculation of diesel passenger car use is limited to EU-28 only and rest of world diesel passenger car fleet is not included (since vast majority of passenger car outside of EU are gasoline fuelled)The industry-standard lubricant fuel economy metric is its performance in the M111 FE test (CEC test L 054 96). In this test the engine is operated at relatively low loads. In real-world driving conditions vehicle engines are typically operated at higher loads where the significance of friction is lower and the impact of a lower viscosity lubricant on the engine fuel economy is concomitantly lower. In recognition of this the fuel economy benefit of the BP lubricants relative to those of the market-average lubricants has been reduced by a conservative factor of 2 (“real world correction factor”)  - this is also a conservative assumption as the divergence from NEDC and real world in EU is 37% worse as reported by the ICCT in 2017 Factsheet (source:
  • M111 industry test model for fuel economy improvements would also count for diesel (it is a gasoline test) - this is a conservative assumption as slower warm-up for diesel engines would make them even more responsive to viscosity changes
  • Vehicles using BP engine oils drive the same annual distance as vehicles using the ‘industry-average’ engine oil.
  • It is assumed that the benefit from reduced friction persists through the service interval on the lubricant.
  • Fuel efficiency performance of a given viscosity grade is the same for both the bp portfolio and the global portfolio since the evaluation uses the mid-point of the viscosity grade upper and lower parameters.


Calculation method

Assuming the correct engine oil is used in the cars, engines using lower viscosity oils burn less fuel than those using higher viscosity oils - this is a well-established effect due to the reduced energy required to move engine components relative to each other.  It is one of the primary reasons why car manufacturers use lower viscosity lubricant in order to help them meet their mandated and aspirational fuel consumption targets.


During the product development process for engine oils, many tests have to be carried out, the results of which determine the performance of an oil against a specification.  One such test is the “M111 FE” test (method reference CEC L-054-96).  This is an ‘industry standard’ test that is established and controlled by the Coordinating European Council (CEC)¹ and used by the Association des Constructeurs Européens d’Automobiles (ACEA) in their European Oil Sequences².  Meeting ACEA specifications can be considered to be a minimum expectation for any oil sold across Europe and into European cars around the world. 

In the M111FE test, the test oil is compared to a known reference oil of (15W-40).  The result is expressed as a percentage benefit over the reference.  In the course of developing oils, BP have run many M111FE tests and have developed a mathematical model relating the viscosity of and engine oil to performance in the M111FE test.  This model has been used to analyse both the global and bp portfolio of lubricants to demonstrate how lower viscosity oils can improve fuel efficiency.


The bp M111FE model requires several inputs:


  • SAE summer viscosity grade (the second part of the xxW-yy grade)
  • 3 viscosity measurements at different temperatures using standard industry methods

Using the above assumptions and processes, the predicted FE benefit of all oils thinner than 15W-40 for the industry global portfolio is calculated.  Then using the percentage volume share of each grade, a pro rata FE benefit was determined for the global 2019 sales portfolio.





The same principle was applied to BP’s 2019 portfolio, using BP sales data, again by viscosity grade. The predicted FE benefit of BP’s portfolio can be calculated and is greater than that of the Industry global portfolio, above.


This benefit is then applied to the fuel consumed by car engines using BP’s portfolio of engine oils rather than Industry global Average portfolio; the % share of engines using BP oils was assumed to match BP’s global market share.


The reduction percentage applied to BP’s vehicle market share translates to approximately 273 million litres of fuel saved versus what would have been consumed if the bp portfolio was the same as the global industry portfolio..

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