Two year's experience or two years' experience or two years experience? [duplicate]

Solution 1:

I believe this is an example of the genitive case. In this situation, an apostrophe is used in lieu of the word of. Thus:

Two years' experience

In lieu of "I have two years of experience."

Chicago Manual of Style 7.24

but,

New Year's Eve (a true possessive)

One-year experience (one-way street)

One year of experience

My experience of one year

My experience from two years ago

Solution 2:

It would be "two years' experience" since it is the experience of two years, which is has to be plural since there are two and can't be "two years experience" because we seldom use plural nouns to modify other nouns. In the same vein, it would be "one year's experience".