Differences between British & American English
ll & l
In British English the 'l' is doubled for verbs ending in a vowel + l. In American English, the l is not doubled.
BrE: travel -> travelled
AmE: travel -> traveled
-our & -or
Words which end in -our in British English often end in -or in American English.
-yse & -yze
Verbs with -yse in British English are spelled -yze in American English.
-ence & -ense
In British English we have -ence and in American English it's -ense.
-re & -er
Words that end in -re in British English usually end in American English in -er.
-ise & -ize
British -ise verbs are always spelled with -ize in American English.
Check also: UK & US - 10 Words That Mean Something Different