Some verbs can have double Ls in the gerund form; for example:
- modeling; modelling
- traveling; travelling
Which form should we use, or which form is used more in the literature?
Actually, to my understading, the form with double l (e.g. “travelling”) is more common in British English, while in American English the spelling would be with single l (“traveling”).
It seems that Irish, Australian, NZ, and Canadian varieties generally prefer the (British) double l versions.
More information e.g. at the Wikipedia article on British/American spelling differences.
(Do note that the opposite also happens: “there are words where British writers prefer a single l and Americans usually use a double l”.)
So, there is no all-encompassing answer to “which form should we use” – it depends on the context and your preferences. Due to the sheer number of American English speakers, the single l versions are overall “more common in literature”, of course. (But when deciding which you should use, do pay more attention to other factors, such as your geographical location or the preferences of your audience.)