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Given a scheme $X$ with structure sheaf $\mathcal{O}_X$, we can associate to each $\mathcal{O}_X$-module $\mathcal{F}$ its global sections $\Gamma(\mathcal{F})$, which gets the structure of a $\Gamma(\mathcal{O}_X)$-module.

Suppose $\mathcal{F}$ is a vector bundle on $X$. Is then $\Gamma(\mathcal{F})$ a projective $\Gamma(\mathcal{O}_X)$-module of finite rank?

Here are two examples, where it works:

• If $X$ is an affine scheme, then a quasi-coherent sheaf is a vector bundle iff its global sections are a projective $\Gamma(\mathcal{O}_X)$-module [of finite rank, as Fred Rohrer pointed out].
• If $X$ is a projective scheme over some field $K$ and $\mathcal{F}$ an arbitrary coherent sheaf on $X$, then $\Gamma(\mathcal{F})$ is a free module of finite rank over the ring of global sections $\Gamma(\mathcal{O}_X) \cong K$. Under some restrictions, we can here also replace the field $K$ by a more general ring.

I would guess that it works in general if the natural map $X \to Spec \Gamma(\mathcal{O}_X)$ is locally free of finite rank [edit: and surjective] or something like this. Probably this fails in general, but I have not yet a (reasonable) counter-example. I am mainly interested here in the case of a quasi-projective scheme over a (not-necessarily algebraically closed) field of characteristic zero, so I would not only be interested in counter-examples but also positive answers to my question for a reasonable subclass of schemes.

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Given a scheme $X$ with structure sheaf $\mathcal{O}_X$, we can associate to each $\mathcal{O}_X$-module $\mathcal{F}$ its global sections $\Gamma(\mathcal{F})$, which gets the structure of a $\Gamma(\mathcal{O}_X)$-module.

Suppose $\mathcal{F}$ is a vector bundle on $X$. Is then $\Gamma(\mathcal{F})$ a projective $\Gamma(\mathcal{O}_X)$-module of finite rank?

Here are two examples, where it works: