Why did boomtowns spring up throughout the west?

In the kingdom of saudi arabia the government controls every aspect of oil production which makes up the majority of the country's economy. while other businesses are owned by individuals, the biggest segment of saudi arabia's economy is oil production. saudi arabia's economy would best be described as a) entirely market. b) almost entirely command. c) a mixture between just market and traditional. d) a mixed economy with large amounts of command.