A plan by Oman is being closely watched by other governments in the region that are preparing for a future beyond oil.

The concept of an income tax has long created debate and anxiety among the citizens of the fossil fuel-rich countries in the Persian Gulf. But no nation actually introduced one until last week, when Oman announced that it would apply a 5 percent tax starting from 2028 on those who make more than 42,000 Omani riyals, or around $109,000.

Officials said that the new tax was intended to promote social equity and reduce the country’s dependence on oil and gas, which made up around 70 percent of the state revenues last year. But Oman could also become a testing ground in the region, where the royal families that have ruled for decades have used their resource wealth to subsidize citizens’ lives while granting them minimal political participation.

Since oil was discovered

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