Yn 2007-2008, ailwerthusodd Asiantaeth y Swyddfa Brisio y rhestrau trethi ar gyfer porthladdoedd yng Nghymru a Lloegr gan arwain at newid yn y sail a ddefnyddir i brisio a rhestru porthladdoedd o ran trethi annomestig gan ei gysoni ag arfer prisio sefydledig wrth ymdrin â busnesau eraill. O ganlyniad, yn lle prisio a rhestru porthladdoedd fel un eiddo, a pherchennog y porthladd yn atebol am dalu'r trethi, rhestrwyd pob eiddo busnes unigol yn y porthladdoedd a'u prisio'n unigol a gwnaed perchennog pob eiddo yn atebol am dalu'r trethi. Mae hyn yn debyg i'r dull a ddefnyddir mewn perthynas â busnesau mewn meysydd awyr neu ganolfannau siopa er enghraifft.
In 2007 - 2008 the VOA undertook a revaluation of the rating lists for ports in England and Wales which resulted in a change to the basis upon which ports were valued and listed for non-domestic rating, so as to make the valuation practice for ports consistent with that established for other businesses. Consequently, instead of ports being valued and listed as one property, with the port owner being liable to pay the rates, the individual business premises located in the ports were listed and valued individually, and the occupier of each property became liable to pay the rates. This is similar to the approach used for businesses occupying airports or shopping centres for example.