The registration plate '6 O' has sold for £100,000 at the DVLA's latest auction of private registrations.
The plate was bought by Ghanim al-Hadaifi, 24, who has already bought '4 O' and '5 O' this year for a combined £146,000.
The DVLA has now earned a total of £666,560 selling the first six digits in the 'O series'.
'1 O' sold for £210,000 in January and '2 O' raised £142,000 in March.
Ghanim al-Hadaifi's spokesman said: "Money is not really an issue, he just wants the best registrations he can have for his cars.
"He already has his sights set on numerous others, which we hope will be auctioned next year."
The most expensive registration sold this year was '1 D', which raised £352,000 at auction.
All money raised from the sale of private registrations goes to the UK Treasury.