The most common Mobil globes, and probably one of the most common in the hobby, are the 13.5" Mobilgas and Mobilgas Special globes. These are found with both blue and black lettering as mentioned before. The Hops or Scott B. can correct me if I'm wrong, but I don't think the lettering color really affects value anymore. It used to be the black versions were more difficult to find, but I don't think it translates to adding a premium to the value of the globes anymore.
Black lettered Mobilgas....



Black lettered Mobilgas Special....



Blue lettered Mobilgas Special with original box. This was listed on Ebay as a reproduction at a very cheap buy it now. I don't know about you, but I don't think too many modern boxes are marked that they were shipped by the Railway Express Agency, lol! wink



Darin Sheffer
Always looking for Mobil and Marathon items I don't already have!