I contacted an old Pennzoil guy who had collected from about 1987 thru 2004, that I had met through eBay in order to find out what I could about this round "O".
He sent me this picture, which I then looked up in the Tom Allen American Oil Cans book. The book places it in the 30's but does not get any more accurate than that. It is the only can in the book with this round "O" that I could find.
What's strange though is on the front of the can , which was shown in the book but not pictured here, the main logo has the classic squared "O". This round "O" only appears in this secondary logo on the back of the can.
He also sent this sign picture with the round "O" but no date.
So this deosn't do a whole lot as far as dating your sign, it's just another piece of the puzzle.
Last edited by SC62; Fri Mar 29 2013 03:09 AM.