Is a sigma 150-500mm lens compatible with a Nikon d3100?

Is a sigma 150-500mm lens compatible with a Nikon d3100? - 1

It's not the make, size or type of the lens that matters (in what comes to compatibility with a particular body), but what sort of mount (coupling) it has.

If you buy it with a Nikon mount, it will work just fine.

Yes, but is not the most ideal solution.
see

If you buy one with Nikon mount, then yes.

If not then no.

As long as you get it with a Nikon mount. If that is a relatively new lens, check if it has an internal motor. If none, it will not autofocus with your camera. If it's an old lens, it would probably not autofocus with your camera. If it's really old, the lightmeter might not even work.

I presume you are reading about this lens from a retailer? I hope!

Every description of a lens for sale lists the mounts the the lens comes in.

I'm sure that all Sigma lenses come in mounts to fit the current crop of Canon, Nikon, and no doubt Pentax DSLR's.

You just specifiy the lens mount you want when ordering the lens.

Yes, Sigma makes this lens for the Nikon system. It has an internal focusing motor so it will work on your D3100 just fine.