I have 149 saved pictures of Pennzoil ads. The first time I see the owls show up is 1937 and the last time is 1942. Shown below. 37 on left. 42 on right.
Now the accuracy of the dates on these is only as good as the source where I got them. They are not dated.
Not that its definitive, but I do have several ads from 1936 and several from 1943 and none of them have the owls.
But if this info holds true, it seems the owls were a short lived campaign.
Now from the book, American Oil Cans, it shows the first can with owls being the Streamliner can but only dates it as being from teh 30's. And the last can it shows with owls is the United Airlines can and it calls this as being from teh 40's. It does not get any more specific than that.
Hope that helps.
Maybe someone else has further info.
Last edited by Steven C.; Sat Jun 16 2018 10:08 AM.