The last fuel protests sparked an immediate 5% fall in the price of larger petrol cars and Glass's Guide believes the same could happen again.
Oil prices have already risen by around 25% since the end of 2003, and the Government has confirmed there will be a 1.92 pence increase in fuel duty in force from the start of September, which was announced in the Budget.
But there is disagreement over what price problems might mean for diesel sales. Jeff Paterson, senior car editor at Glass's, said: 'We are already witnessing a marked rise in the popularity of diesel cars, and their share of the total UK new car market is only likely to rise further still as discontent about fuel prices intensifies.
'The growing popularity of new and used diesel cars will be particularly noticeable in the large saloon and SUV sectors where petrol consumption levels are at their highest.'
But dealers who expressed an opinion in a CAP survey recently were already experiencing or expecting an increase in demand for diesel engines no matter what happens with the fuel prices.
In all, more than 10% of dealers cited continued growth in diesel engine popularity as a major impact of fuel price increases.
Just short of 10% questioned in a survey carried out during April, before the latest price increase, reported greater customer interest in smaller-engine cars across the whole market, without a preference for fuel type.
But a common thread throughout the survey was the view that, whether or not petrol price increases are likely to significantly affect car buying habits, tax issues and interest rates had the most noticeable impact.