And JD Power-LMC says that even this average hides the differences between countries in Europe with France showing a figure of more than 60%.
The survey questions whether the success of diesel in Europe can be replicated in other parts of the world.
Explaining the success of diesel in Europe, the study says: 'In many European countries, the tax burden on diesel fuel is much lighter than on petrol. Those countries (such as France) in which the disparity is the greatest have, not surprisingly, been in the forefront of the switch to diesel.'
'In addition, all types of fuel are subject to much heavier tax rates in Europe than in other European markets. Thus, in the UK, where the tax burden is similar on both types of fuel, but very high on both, the fuel economy savings offered by diesel engines have increased their popularity in the recent past.
'But the success of diesel is not just a story about tax. It is also a story of rapid technical progress, which has preserved and enhanced the fuel efficiency advantage enjoyed by diesel cars and which has removed many of the negative perceptions held about diesel in the past.'
The study adds that since the switch to electronic fuel injection the leap in petrol engine technology has been 'far less significant'.
'The move to direct injection for gasoline looks likely to provide a similar boost to efficiency, but it is still some way from fruition, and not yet a totally proven technology.'
It adds that there is 'still some way to go' before diesel emissions are at the same level as petrol but says any moves that may eliminate this disparity are a key issue for the global future of diesel light vehicles.