Exceptions to spelling rules are common on both sides of the Atlantic. Therefore, when in doubt, the UOC recommends using the preferred spelling provided in the Oxford Dictionary (British and World English version) for BrE and the preferred spelling provided in the Merriam-Webster Dictionary for AmE. Please note that, unlike many other authoritative BrE sources, the Oxford Dictionary uses the -ize spellings of words like organize and maximize. For more information on this difference, see the relevant section below. 

Notwithstanding the plethora of exceptions, some of the most common differences in BrE and AmE spelling conventions are listed below:

BrE has retained the digraphs -ae-and -oe- in certain words of primarily French, Latin and Greek origin that AmE spells with a bare e. Examples:

However, some words can be, and often are, spelled with the digraph in AmE, too, although the bare spelling is also accepted. Examples:

Likewise, certain words may be spelled with either the digraph or the bare in BrE. Examples:

As a general rule, the UOC prefers to follow Oxford spelling (e.g. aesthetic, archaeology and oestrus but medieval), although the overarching rule is always to be consistent throughout your text. When in doubt, check the Oxford Dictionary.

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BrE generally uses the spelling -ce for nouns and -se for verbs. Examples:

AmE preserves this distinction with some words (e.g. some advice but to advise) but in other cases always uses -se(e.g. defense, license, offense)

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Unlike AmE, BrE retains the final silent in certain words when adding suffixes. Compare:

Nevertheless, for some words, both spellings are accepted in both AmE and BrE. AmE tends to be more flexible than BrE in this regard. Examples:

Note, however, that in legal contexts, the spelling judgment is generally preferred in both AmE and BrE.

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While BrE often prefers to spell this and related suffixes (-isation, -ising, etc.) with an s, AmE uses only the version with z. Compare:

This notwithstanding, the Oxford Dictionary prefers to spell these words according to their etymological origin, the Greek root -izo, and thus also uses the spelling.

Similar differences are found with the suffix -yse/-yze. Compare:

In this case, the Oxford Dictionary uses the spelling, as these words are formed from a different Greek root, lyo, rather than from -izo. For more information on Oxford spelling conventions, see the Wikipedia entry Oxford Spelling.

Separately, please note that some words are always spelled with an in all varieties of English. This is generally because the -ise is actually part of a longer component of the word, such as -cise, -prise or -vise, rather than a separate suffix in itself. Nevertheless, a smaller group are always spelled with z. Examples:

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BrE generally doubles the final before adding -ed, -ing, -er, -est or -or in words with an unstressed final syllable. AmE generally does not. Examples:

In contrast, BrE often uses a single l in words formed from monosyllabic root words ending in ll and many of their derivatives, whereas AmE generally retains the double l. Compare:

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BrE generally uses the ending -ogue, while AmE generally prefers -og. Compare: 

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Words ending in an unstressed -our/-or in which the vowel sound is reduced (i.e. the ending is pronounced -er) generally take a in BrE but not in AmE. Compare:

The u is used in AmE, too, when the vowel sound is not reduced (i.e. when the ending is pronounced -or). Examples:

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Certain words, mainly of French, Latin and Greek origin, that originally ended in a consonant + -re retain that spelling in BrE but are spelled with a final -er in AmE. This mainly occurs in words in which the -re/-er is unstressed and is particularly common when the preceding consonant is a or a t. Examples:

Note, however, that BrE uses metre for the unit of length, but meter for the measuring instrument.

Likewise, some words retain the original -re spelling in AmE, too, particularly when it is preceded by a or when the original French pronunciation has been retained. Examples:

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In BrE, the past forms of certain verbs may be spelled with a -t or -ed, whereas in AmE they almost exclusively end with -ed. Compare:

That said, both spellings are understood and accepted in both BrE and AmE. In general, it is UOC policy to use the -ed form. Example:

Note, too, that BrE and AmE tend to use different forms for the past participle of the verb to get. Whereas BrE generally uses the forms get-got-got, except in certain set phrases (e.g. ill-gotten gains), AmE generally uses get-got-gotten, except with the possessive have got (e.g. I've got three pens). Compare:

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While both -wards and -ward can be found on both sides of the Atlantic, BrE tends to favour -wards, while AmE tends to favour -ward. Thus:

This is particularly true when the words being formed function as adverbs. In contrast, when they function as adjectives or as part of a phrasal verb, the suffix -ward generally prevails on both sides of the Atlantic. Examples:

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In addition to the above, several common words that do not fall into any of the above categories are also generally spelled differently in BrE and AmE. These include, among others:

Finally, the words while and among may also be written whilst and amongst. Although the -st spellings are more common in BrE than in AmE, both variations are accepted. In general, the UOC prefers to use the simplified spellings while and among. As always, however, the most important thing is to use them consistently within your text. 

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