Jail 或 Gaol (新!)

Question: I am confused by the words jail and gaol; do they mean the same thing? Are they pronounced differently?

Grammar:

They both mean exactly the same thing; prison.

He was sentenced to ten years in jail.

Peter has spent more than half his life in gaol.

They are also pronounced in exactly the same way. Likewise with jailer and gaoler, which both mean prison guard:

I asked the jailer for some water.

My gaoler locked the cell door.

In the UK we use both, so, for example, a famous poem by Oscar Wilde is written as “The Ballad of Reading Gaol”.

However in the States they only use the jail form; one of Elvis Presley’s biggest hits, which later became a film, is Jailhouse Rock.