Yes, they are supposed to run on 98 ron unleaded, which means (as you expected) you should be splashing out on a fuel such as optimax (now called V Power) or BP Ulitimate. I believe that Tesco also do a 99 ron unleaded, but Iv never tried it. When I first got mine I tried it on regular unleaded, and it didnt like it, so Iv been running it on V Power ever since, especially now since Iv got a modded cylinder head with Shricks!