Oil can shape
As an Ex-member of Mrs. Windsor's Flying Circus, I would like to add my tuppence worth to this thread.
As a trainee I and the others were taught, under threat of death or worse, before you unscrew the cap - check the contents. All aviation liquids came in 1,(square) 5, 50, (both round) Imp Gall containers, be it oil - hydraulic - vegetable mineral or synthetic, engine, lubricating, de-icing fluid or whatever. If I recall correctly, the only 'commercially' labelled product was Racasan. All containers were the same shape, mistakes were made e.g. the wrong hydraulic fluid being added to a system.
Later in my service, I spent time as a trade examiner and when testing a young lad, I asked 'You are servicing a hydraulic system requiring OM-15 and you find a gallon can marked OM-15 in the hangar. It is half full with a red fluid but has no cap. Would you use it?' This was a standard question and the expected answer 'No, because it could be contaminated.' The answer I received was 'No, because you said it was half full. That means I would be adding air to the system and I would then have to bleed it.' I carried on with the test and asked him at the end how long was his training and what had he been taught about fluid contamination. He looked at me as though he was seeing water burn. OK 18 weeks is a lot less than three years, but I am certain flight safety was never overlooked.
I have to agree with everyone who puts the oil mix up down to insufficient training. It has nothing to do with suppliers. At the end of the day it is the man/woman who actually does the pouring who carries the can, (no pun intended).
Also as 'The 'tiffy' says in civvy street, all our cans are round except for the 1US gall cans of Skydrol. And, for the man who says it is due to transport costs the round quart cans are shipped in - you've guessed - square boxes. Every manufacturer has a different colour, not every product, but they do have their own identity printed on the can.
My only advice is spend an extra few seconds reading the label. It might not just be the saving of a promising career - just think of the life/lives you have saved and, not the 40 pence and an on-time departure.