Driving from Mostar into Croatia or Montenegro is a practical day-trip option for travelers based in Herzegovina, but cross-border use of a rental car depends on written authorization, insurance class, and the border you choose. Most rental desks in Mostar Centar and near Mostar International Airport (OMO) require cross-border permission in advance, and many suppliers will only approve travel with Zero Excess or full coverage plus a physical Green Card for specific routes. For many visitors renting in Mostar, a physical Green Card is not required on a Bosnian-registered rental car because Bosnia and Herzegovina joined the License Plate Subsystem of the Multilateral Guarantee Agreement on 19 October 2020. That system means the vehicle’s BiH registration is generally accepted as proof of third-party liability cover for many regional crossings, including Croatia and Montenegro, when the rental company has issued cross-border permission. Total Croatia News reported in 2026 that vehicles registered in the 33 EU/EEA countries plus Switzerland, Liechtenstein, Andorra, Iceland, Norway, and Serbia do not need a physical Green Card when entering or leaving BiH. That matters for most Mostar rental fleets because local suppliers such as rent.ba (CityRent), Carrus, Nur Rent A Car, MANDI Rent A Car, Rent A Car Champion, E&G Rentacar, Yes.ba, Sixt BiH, Hertz, Europcar, Avis, Wheego, CarWiz, Surprice, Green Motion, Drive365, Trio Rent a Car, and Hyundai Rent a Car generally operate Bosnian-registered vehicles. A physical Green Card is still required for some non-EU or non-licence-subsystem vehicles, and drivers entering BiH without valid insurance documentation can face a 300 KM fine, according to a 06 August 2025 report from paragraf.ba. Cross-border authorization from Mostar is a paid add-on, and the fee usually depends on the destination country, the number of borders covered, and whether the supplier bundles CDW, SCDW, or Zero Excess into the permit. Rental desks commonly collect the charge at pickup, and many operators also place a pre-authorisation on the card for the deductible or excess. For price-sensitive trips, the cheapest structure is usually a single-country permit for Croatia or Montenegro, while multi-country Balkan loops that include Serbia or Republika Srpska routes can push the permit price higher. If you are planning a coastal route via the Pelješac Bridge or a return through the Neum corridor, check whether the contract treats that journey as a cross-border event or a domestic transit through Bosnia and Herzegovina. Most rental companies in Mostar treat Zero Excess as the safest cross-border option because foreign-road claims can trigger a deductible, a claim review, and a card hold. CDW covers collision damage up to the policy limit, but SCDW or full coverage is what usually removes the excess and reduces the renter’s out-of-pocket risk to zero. Drive365 BiH stated in a policy update published on 04 June 2024 that if Cross-Border and Territorial Restrictions are violated, all protections lose validity. That wording makes the contract terms more important than the road conditions, and it is why suppliers such as Drive365 and Yours Car often refuse to issue a cross-border permit unless the renter accepts Zero Excess. A typical Bosnian rental CDW policy can still leave a €500 or higher deductible on the renter’s card if damage occurs abroad without the correct add-on. In addition, some suppliers charge an administrative fee of €40 or more, and airport collection points near OMO may add a pickup surcharge. For travelers comparing protection levels, the safest setup is full coverage plus written cross-border authorization rather than relying on standard CDW alone. If a rental car from Mostar is damaged in Croatia or Montenegro, the driver must treat the incident as a formal insurance case, not a roadside exchange of details. The most important steps are police notification, documentation, and compliance with the rental company’s claims process in Mostar. In Croatia, the driver must call the police and obtain an official police report, or “policijski zapisnik,” for any damage event. Croatian procedure also includes an alcohol breath test for involved drivers, and refusing that test can invalidate the claim.