1* It depends upon what part of the country you reside in.
If I were to purchase off road / farm diesel I would have to purchase a minimum amt. @250-300 gallons which would have to be delivered.
2*In my area there are no fuel stations that carry off road diesel like there are in say Kansas or Oklahoma for example.....so if I were to use 300 gallons in a year then yea it would be cheaper,
3*but for my 30- 60 gal I may use in a year it is not practical.
4**Oh yea I would also need a tank to store it so there is a cost for that too.
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*So the moral to this story is.....no it is not cheaper for everybody.