Spelling of "moustache"

This seems like a good one for Ngram.

It looks like in British English moustache has always been the preferred spelling.

In American English, it's been more of a battle with mustache now in the lead.

So here's a combined view. Both are contenders in the English-speaking world, but clear preferences exist on opposite sides of the pond.

(Have to wonder if the peaks and valleys correspond to mustaches going in and out of vogue.)

Both spellings are correct. Which is more standard will depend where you are. Mustache is somewhat more common in American English, and has been since the 1940’s. Moustache is older (being the original French spelling, from which the English word is derived) and still much more common in British English, to the extent that mustache may be seen as an Americanism; but mustache is now gaining some ground in Britain too.

(Sources: Google N-grams viewer for usage, and the OED for etymology.)