Different style guides give different answers so you'll find someone to support most any way you decide to go.

There is currently a bill in the Arkansas state legislature to give a final determination on whether the possessive of Arkansas is Arkansas' or Arkansas's.

AP style guide requires always adding 's to a singular noun to make it possessive. The New York Times styleguide would have you using Productions' without another s. The Chicago Manual of Style uses 's unless the final S in the singular noun is silent (Camus, Francois, Arkansas).

Way too much detail here.

So the key is to pick a style and just be consistent with it.

As Alex said, you'll find different style guides with different answers regarding proper names. On top of that, you'll see the same style guide give a different answer depending on the name (using the "Whichever sounds better" rule).

Examples:
Most guides will have "Jesus'" rather than "Jesus's".
Jones' vs. Jones's can go either way.

It goes on. When something that's singular ends with an 's', the standard rules go out the window. There's the added gray area in this particular case because the individual word the apostrophe is being applied to is plural, but the conceptual unit it's being applied to is singular.

So in the end, it's about picking one and being consistent.

Thank you to all who responded (and who may continue to respond). I guess the definitive answer is that there is no definitive answer.

Yep, GD is right. Pronunciation is the key. I love that he used Jesus's as the example, and the one I've seen cited most often is Moses's. Heheh.

It depends on the style guide for whichever company employs you. Mine, for instance, is s-apostrophe in all cases. Although it can be debated, I think you'll find that most of the standard printers and newspapers almost always side with s-apostrophe.

I know MBC discovered recently that there's a semi-accepted standard to use s-apostrophe-s for religious figures (Jesus's, Moses's, etc) but I think that's pretty silly.

Also, there's a general guideline my team follows in the face of such situations. If there's something that could be debated as to how it's stated, rephrase! If "I just visited XYZ Productions' website" gives you pause, say "I visited the XYZ Productions website" instead.

I think Eats Shoots and Leaves says this breaks down according to English vs. British. I don't recall which is which, but one side will say Mr. Jones'; the other, Mr. Jones's. I think both agree that plural is simply s', e.g, the dogs' bones. Your example complicates matters because it is a name that ends in a plural. I would go with s' or, more likely, try to evade the problem as LSPE outlines above. To be even more uncontroversial--or less controversial--you might say "the web site designed for/run by/etc. XYZ Productions."

My first thought is -- what kind of name is XYZ for a company? Is it short for Examine Your Zipper?

I would use s' for written, but probably pronounce the extra s sound verbally.

Ah, but that's just it. If the name is pronounced "Joneses," that's when you are to use Jones's.

Most times, the pronunciation does not change when possessisizing a word ending in "S" - and so the more common s' is proper.