How does life in yemen and oman differ from life in saudi arabia?

One big difference between the two is that Saudi Arabia has very abundant oil reserves, which are the basis of its economy, and Yemen and Oman, despite being next to it, have very small oil reserves.
This also influences how rich the countries are, although in the recent years Oman is catching up on Saudi Arabia and it's not very poor.

Themes; subfields is the answer