if i had to guess id say a euro gallon was 5ltr, just rounding the metric conversion. however a net search provides the answer. a euro/uk gallon is 1.2 us gallons. so its a imperial gallon. lol bet that winds up the metric mob
I've also heard of "euro" refer to a style of tank over here in the states also. One that has a bowed front pane but not bowed a lot like a "bowfront" tank so they call it a "euro" (I believe).