Used economically, the oil should last for five days

Hello, native English speakers,
I need your help.
I'm grading the exam paper now.
A student wrote：
Used economically, the oil should last for five days
instead of "Used economically, the oil will last for five days."
Would that be possible? Would it have almost the same meaning?

Hirashin

They are both fine and are virtually identical, with the only difference being the slight qualification inherent in "should" as opposed to the more definitive "will".

In all honesty, the 'should' version sounds more natural to me. When predicting how long something with a variable consumption rate will last, 'will' can be a bit too strong of a term.

It depends, of course. If the speaker is extremely confident in their estimate of the situation then they'll use 'will' to express this confidence. However, in most situations involving imprecise terms like 'used economically' the speaker is going to use 'should' to express some slight room for doubt.

Compare it to, 'if we ration ourselves to 10 gallons a day, the 50 gallon drum of oil will last 5 days'. You wouldn't use should here because it's clearly correct with no guessing or estimating involved.

In the end though, both are correct and which is actually more natural depends on the precise situation the sentence is used in.

(Hmmm. I'm not sure I added anything, I think I just used a lot more words to say what Majestic already said.)

Thank you for the help, Majestic and SomeCallMeChris.

Chris, your explanation about "will" is enlightening to me, thank you.