Three more car hire websites have committed to providing full charges upfront following enforcement action by the competition watchdog.
Online travel agent P&P Associates and the operators of price comparison sites Affordable Car Hire and Flexiblecarhire.com will include all compulsory charges in their hire quotes under legally binding agreements, the Competition and Markets Authority (CMA) said.
Under the agreement, their initial quotes must include mandatory charges like fuel surcharges, young driver fees and out-of-hours pick-up charges if applicable.
They must also show all essential information such as any deposits and insurance excesses, policy on fuel charges, and what exactly the insurance covers.
The CMA said the three businesses co-operated fully with the action, which it launched after an investigation into whether certain sites were complying with consumer protection law.
The move follows the CMA's industry-wide review of car rental price comparison sites, which found many were advertising very low prices to customers by not including all costs.
CMA executive director for enforcement Michael Grenfell said: "It is important people know what they're signing up to online when hiring a car. Prices must be transparent and include all compulsory costs so that people can find the deal that's best for them.
"The CMA's work over the past year has vastly improved the sector and brought the majority of sites offering car hire in line with consumer protection law. UK customers can now be more confident that what they see is what they will pay."
The CMA said it was also now taking enforcement action against businesses based overseas but selling directly to UK customers online.
It follows reports by UK consumers of hidden charges for fuel, surprisingly high excess amounts and hidden insurance costs.
Mr Grenfell added: "This move sends a clear message: just because a business is not on UK soil doesn't mean the law doesn't apply when it sells in the UK.
"British consumers have a right to protection under consumer law and the CMA will work to ensure they receive it."