Older the better.....IMO the majority of maps from the late 40's to the 70's are mostly a dime a dozen. Out of the companies you mention, all are plentiful major oil companies. Look for small independent or regional oil companies, those are the ones that have more value, even later ones. Also, what collectors call "graphic maps" with lots of attractive artwork that usually run the 3 main panels when a map is initially unfolded are collectible, generally these are earlier maps as well from the 30's or before. Good luck....
Darin
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