The average gross national product (GNP) per head in the six Arab states in the Gulf area is 11 times higher than the average in the other 16 Arab states. 
Of the Arab states, the Gulf ones have 14% of the population, 60% of the output, and an average GNP per head similar to the figures for EU members Spain and Malta.
The others have 86% of the population, 40% of the output, and an average GNP per head similar to those in the poor sub-Saharan African countries the Ivory Coast and Lesotho.
Of course it is possible to conclude too much from this comparison. Bear in mind that Lebanon has almost two-thirds of the GNP per head of Saudi Arabia, while Qatar has the world’s largest, equal to four times the Saudi figure. And there are different ways to calculate output too.
1) An Arab state is here defined as a member of the Arab League. The Arab Gulf states are the six members of the Gulf Cooperation Council: Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates . Excluding Oman, they are in the world’s top 15 countries by GDP per head when it is calculated by the purchasing-power parity method. (That is not the method used above; by the PPP method, average GDP per head is higher in the Arab Gulf states than it is in the US, Switzerland and Norway). When Oman is included, they are in the top 25. The other Arab states are Algeria, Comoros, Djibouti, Egypt, Iraq, Jordan, Lebanon, Libya, Mauritania, Morocco, Palestine, Somalia, Sudan, Syria, Tunisia and Yemen.
2) Some count Iraq as a Gulf state. But having been ravaged for 36 years by war and by the effects of war and sanctions, Iraq differs considerably from the six countries mentioned. It has a smaller GDP per head than the Lebanon – slightly smaller or considerably smaller, depending on the calculation method used.