The population could be 3.8mn and 3.6mn as per medium-fertility and low fertility assumptions respectively.
Gender wise, the number of Omani men is expected to grow by 69 per cent while women will record a rise of 72 per cent, according to average fertility assumption for the year 2040.
As per the high fertility method, children under 15 years of age is expected to reach 30 per cent of the total Omani population in 2040, while low fertility assumption estimates the share to be 25 per cent.
Also, 11 per cent of the Omani population will be children aged under five years (high fertility assumption), against nearly eight per cent at present, according to low fertility assumption.
The study also projects that youth (aged 15–29 years) will make up about 27 per cent of the total Omanis, marking a three per cent decrease compared to figures for mid-2015.
Further, the number of Omanis in the working age (15 till 64 years) will constitute 64 per cent and 69 per cent, according to high and low-fertility assumptions respectively. It is also expected that Omani women in childbearing age will constitute 45 per cent of the total in 2040, according to medium fertility assumption.
Giving details of dependency rates, the study indicates 56 dependants per every 100 people in the working age by 2040 (high fertility assumption).
The figure, however, decreases to 45 dependants as per low fertility assumption.
The study says that the largest projected increase (322,000) during the next 25 will be recorded in Muscat governorate, assuming the policy of reducing the number of expatriates will continue.
However, the size of the young people (less than 30 years of age) in Muscat will decrease by 13 per cent by 2040.
In contrast, the lowest projected increase in the population is expected in the middle of 2040 in Musandam with an addition of just 17,000.
Muscat and North Batinah will be home to 41 per cent of the total Omani youth population in the age group 15-29 years; while two-thirds of the Omani children under five years (constituting 66 per cent of the total) will be residing in Muscat, South Batinah, North Batinah and North Sharqiyah.
Generally speaking, even as it is assumed that the total fertility rate will decrease over the projection period, the population is set to increase across the three assumptions. This is called the Population Momentum - which says that population growth will continue despite declining fertility rates.
The study also shows that the Omani population pyramid during the projection period moves closer towards achieving the demographic window by 2040. It is the stage in which the community reaches its peak population size in the working age compared to the lowest percentage of dependent population (children and old people).