Currently, arrival regulations in Oman for tourists include a requirement that the vehicle in which they travel is insured for the territory of Oman.
Insurance may be either taken by having the vehicle’s policy include Oman, this generally is done for regular visitors from the UAE. The alternative is to purchase specific vehicle insurance for any visit. These policies can be obtained at all land borders.
It looks as if a similar mandatory policy for Oman Tourist’s Insurance will be introduced for all tourist visitors to Oman alongside with compulsory insurance for all residents. This is comparable to the Schengen Countries and others where insurance is mandatory though currently, UK visitors as they are also currently covered by reciprocal EU/UK health cover don’t seem to be required to have this. Other countries which look as if compulsory insurance will be ramped up include the UAE, Qatar and Turkey. The Foreign Office in the UK gives an overview of international insurance.
If you are visiting Oman my rewrite of the Brandt Guide to Oman is available on Amazon