Words such as organize and organise can be written with z or s, with US English using the z form and British English using either z or s. For example:

US English British English
organize organize or organise
organizing organizing or organising
organized organized or organised
organizer organizer or organiser
organization organization or organisation
recognizable recognizable or recognisable

When writing in British English, therefore, you should decide whether to use the z or s spelling, and use the same dictionary or spelling checker throughout for consistency (though see below). In choosing which to use, you should follow any style guidelines of your university, publisher or target journal.

If you wish to make your text more international, using the z spelling reduces the differences between British and US English. In fact, z is the standard British English spelling in the Oxford English dictionaries for example.

Unfortunately, for UK English your word processor may not distinguish between s and z spellings, making consistent computer checking of your document more difficult.

Words pronounced z but written with s in both British and US English

Neither British nor US English uses z or s spellings consistently – both use z and s to varying extents. A list of words that are pronounced z but always written with s, in both British and US English, is given below:#

advise arise chastise
circumcise comprise compromise
demise despise devise
disguise enterprise excise
exercise expertise franchise
guise improvise incise
liaise likewise malaise
miser noise otherwise
poise praise raise
revise rise succise
supervise surmise surprise
televise treatise turquoise

Words always written with ys in British English

British English US English
analyse analyze
catalyse catalyze
dialyse dialyze
electrolyse electrolyze
hydrolyse hydrolyze
paralyse paralyze
pyrolyse pyrolyze


lyse lyse