Here is some input from an old friend who was a REME SgtMjr in the 40's.
"Both photographic evidence and logical considerations clearly speak against the use of petrol barrels. Have you ever tried to load a barrel full of petrol on a truck with pretty high ground clearance without using a forklift?
It should also be noted that vehicle fuel throughout the war was issued to British troops in the dreaded 'Flimsy' cans, stowed four in a small wooden crate.
While every Allied quartermaster was more than happy when a German supply depot was seized and a couple hundred Jerrycans fell into his hands (the Jerrycan being the only useful design for carrying petrol in those days, and still being used to this day).
There was also a War Office Memorandum that dictated that all cans containing fluids must be painted according to an approved list. I cannot lay my hands on a copy anymore, and memory is failing me. But I do remeber that Black or Black with a white X was drinking water. Green and Blue were lubricating oils. Yellow was primarily for foodstuff, cooking oils, vinegar etc. Red was always dangerous or corrosive fluids, with a number of coloured X's to indicate particular contents. Petrol was for the most part shipped in unpainted cans. Of course the rules were rarely followed once in a field location.
As an aside, we would often use a flimsy of petrol to chill a beer. Bury the beer bottle 18" into the sand, pour all the 4 gallons of petrol over the hole and wait 30 minutes, for evaporation, not icy cold but very refreshing, and highly illegal.
The current NATO Jerrycan was designed as a combination of the original German design, and as a result of having to develop airdrop cans. Neither the Jerrycans or the earlier "flimsies" were suitable for air-dropping. Firstly their rectangular shape would have required a new type of drop container to be designed and secondly it was found jerrycans could split open if hard contact with the ground was made (flimsies werent even suitable for consideration).
To supply remote outposts and irregular friendlies, a new type of can was required that would both fit inside an air-drop canister and be strong enough to withstand a parachute landing.
In 1943 the new design was finalised and production began. Due to the specialised nature of the can, it appears that the government contract issued in 1943 was of sufficient size that no more were made in later years. Note that the cap was borrowed from the German design, and later with a squaring of the shape became the standard of the NATO can."