When was the last time you found a gas cap interesting?

So, Ford has those cool gas caps which are actually environmentally friendly... so I suppose that they could be considered interesting just because of that. But, what about the gas caps of the Mercedes Benz C300? That cap has a yellow ring (see picture after the jump) and tells potential gasoline-pumpers that they must either use premium or E85. That makes sense considering that the E85 fuel actually has a higher octane rating than the premium fuel does.

Getting back to the Ford gas cap -- Since when did Ford recommend BP gasoline? Is there any reason for that other than a marketing deal? I doubt it, but I did think that it was interesting.

[Source: Inside Line]