Five of the biggest car hire firms in Europe have promised to act on customer complaints, following a review by regulators.
The Competition and Markets Authority (CMA) inquiry - supported by the European Commission - looked particularly at insurance complaints.
Some motorists say they feel pressurised into buying excess insurance when picking up a car.
But now the firms have agreed to provide better information in advance.
Avis Budget, Enterprise Rent-a-Car, Europcar, Sixt and Hertz have all agreed to make the changes within six months.
The CMA looked at other typical complaints, including charges for damage to a car - which drivers often say they did not cause.
It also looked at fuel policies, and whether companies require drivers to return a car with a full tank.
The changes will apply across the European Union.
By the end of the year, the five firms have promised to provide:
- better information at the booking stage about which insurance products are optional
- more clarity about the way cars are inspected for damage, before and after the hire agreement
- improved dispute processes when cars are damaged
- an option to return a car with a full fuel tank, should customers wish
The CMA said the changes would benefit motorists hiring cars both in the UK and Europe.
"The improvements by these five businesses now set a benchmark for the rest of the industry to follow," said Nisha Arora, the CMA's senior director.
The consumer organisation Which? said other companies should obey the same rules.
"The hidden costs and sneaky practices of car hire firms have plagued airport arrival lounges for decades," said Richard Lloyd, executive director of Which?
"We now need all rental companies to be totally upfront about charges, so that people know exactly what they will pay when they book."
UK motorists who are in dispute with a car hire company already have access to a conciliation service run by the British Vehicle Rental and Leasing Association (BVRLA).
Such services are being bolstered by new European regulations - which came in last week - on Alternative Dispute Resolution procedures.
The idea is to help people avoid expensive legal bills.
"We believe that our mandatory code of conduct, governance regime, and free, no-obligation conciliation service will provide added peace of mind to people hiring from a company displaying the BVRLA logo," said Gerry Keaney, the chief executive of the BVRLA.
From 2016, the new rules outlined by the CMA will become part of the BVRLA's code of practice in the UK.