The Arabian Peninsula formed as a result of the rifting of the Red Sea between 56 and 23 million years ago, and is bordered by the Red Sea to the west and southwest, the Persian Gulf and the Gulf of Oman to the northeast, the Levant and Mesopotamia to the north and the Arabian Sea and the Indian Ocean to the southeast. The peninsula plays a critical geopolitical role in the Arab world and globally due to its vast reserves of oil and natural gas.
Before the modern era, the region was divided into primarily four distinct regions: the Central Plateau (Najd or Al-Yamama), the Arabian Sea and Indian Ocean Coast (South Arabia or Hadhramaut), the Persian Gulf Coast and Gulf of Oman (Eastern Arabia or Al-Bahrain), and the Red Sea Coast (Hejaz or Tihamah). Eastern Arabia consists of the entire coastal strip of the Persian Gulf and the Gulf of Oman. Hejaz and Najd make up most of Saudi Arabia. South Arabia consists of Yemen, a sizable part of Saudi Arabia ('Asir, Jizan, and Najran) and (Dhofar) in Oman.
(Here’s what I found,Hope it help!)