In writing a blog entry today I used the word "prise" which was promptly underlined in red by the spell-checker.
Just to be certain, I popped it into onelook and this is what came back in the quick definitions.

▸ verb: to move or force, especially in an effort to get something open
▸ verb: make an uninvited or presumptuous inquiry
▸ verb: regard highly; think much of

The first definition here is the ONLY one that I think is valid and is the one that I intended. The second definition seems to me to be of "pry" and the third definition of "prize".

What does everyone else think?

Prise and prize do seem to be variant spellings of the same word. Some dictionaries show the "s" spelling as obsolete in the "regard highly; think much of" sense. The "make an uninvited or presumptuous inquiry" definition does seem to fit pry (or pries) better, though.

Interesting, Bob. I hadn't heard of prise before, but it seems like it means the same as pries, as in "she pries open the jar." How are they different? I checked Dictionary.com, and here is what they said for prise:

1. to force open by levering
2. to extract or obtain with difficulty: they had to prise the news out of him

— n
3. rare , dialect or a tool involving leverage in its use or the leverage so employed

Now, pry isn't a tool, though that was a rare use anyway. Otherwise, they seem to mean the same thing. Are they different words or just variants of the same word?

Because I'd use it as "She prises open the jar" and in the past "prised" rather than "pried"

Interesting. I've not seen or heard prize (as a verb synonymous with pry) in General American English. The OED1 (which gives 1686 as its earliest citation) says it is a denominal verb from prize (noun entry 4) meaning "1. An instrument used for prizing; lever. 2. The act of prizing, ; leverage, purchase." This noun comes (via Middle English) from French prise 'a taking hold'., which is ultimately from the verb prendre 'to take'. Pry, meaning "To raise or move by force or leverage; to force up" (chiefly US English, from the ealy 19th century, is given the origin: "shortened from prize, prise, [...] through confusing the final consonant with the -s of the 3rd pers. sing. pres." Very interesting word history.

I am thinking this might be an English/American difference? Arnie, would you say you "prised" open a jar?

You may well be right that it's a British/American difference. I'd be more likely to prise open a jar than pry it open, although the second sense is also known and used.

Since I've not heard of "prise," I'd do nothing else but "pry" it open. I learn something new here every day!